All addEventListener should returns EventSubscription.t

Closes #408

I checked some that currently returns unit:
- PushNotificationIOS doesn't returns a thing https://github.com/facebook/react-native/blob/6677f405a2de0833286671bc308230ea1d574f82/Libraries/PushNotificationIOS/PushNotificationIOS.js#L187
-  Linking too https://github.com/facebook/react-native/blob/6677f405a2de0833286671bc308230ea1d574f82/Libraries/Linking/Linking.js#L38
- Dimensions neither https://github.com/facebook/react-native/blob/6677f405a2de0833286671bc308230ea1d574f82/Libraries/Utilities/Dimensions.js#L103

- and AppState doesn't https://github.com/facebook/react-native/blob/a442e0b63526405249ddf50e58f1fdc618c789bc/Libraries/AppState/AppState.js#L79

Author: MoOx

reason-react-native/src/apis/AppState.md

@@ -22,7 +22,7 @@ external currentState: t = "";
 [@bs.scope "AppState"] [@bs.module "react-native"]
 external addEventListener:
   ([@bs.string] [ | `change(t => unit) | `memoryWarning(unit => unit)]) =>
-  EventSubscription.t =
+  unit =
   "";
 
 [@bs.scope "AppState"] [@bs.module "react-native"]

reason-react-native/src/apis/AppState.re

@@ -15,7 +15,7 @@ external currentState: t = "";
 [@bs.scope "AppState"] [@bs.module "react-native"]
 external addEventListener:
   ([@bs.string] [ | `change(t => unit) | `memoryWarning(unit => unit)]) =>
-  EventSubscription.t =
+  unit =
   "";
 
 [@bs.scope "AppState"] [@bs.module "react-native"]

reason-react-native/src/apis/AppState.rei

@@ -15,7 +15,7 @@ external currentState: t = "";
 [@bs.scope "AppState"] [@bs.module "react-native"]
 external addEventListener:
   ([@bs.string] [ | `change(t => unit) | `memoryWarning(unit => unit)]) =>
-  EventSubscription.t =
+  unit =
   "";
 
 [@bs.scope "AppState"] [@bs.module "react-native"]

reason-react-native/src/apis/BackHandler.md

@@ -5,14 +5,13 @@ wip: true
 ---
 
 ```reason
-type remove = {. "remove": unit => unit};
-
 [@bs.scope "BackHandler"] [@bs.module "react-native"]
 external exitApp: unit => unit = "";
 
 [@bs.scope "BackHandler"] [@bs.module "react-native"]
 external addEventListener:
-  ([@bs.string] [ | `backPress | `hardwareBackPress], unit => bool) => remove =
+  ([@bs.string] [ | `backPress | `hardwareBackPress], unit => bool) =>
+  EventSubscription.t =
   "";
 
 [@bs.scope "BackHandler"] [@bs.module "react-native"]

reason-react-native/src/apis/BackHandler.re

@@ -1,11 +1,10 @@
-type remove = {. "remove": unit => unit};
-
 [@bs.scope "BackHandler"] [@bs.module "react-native"]
 external exitApp: unit => unit = "";
 
 [@bs.scope "BackHandler"] [@bs.module "react-native"]
 external addEventListener:
-  ([@bs.string] [ | `backPress | `hardwareBackPress], unit => bool) => remove =
+  ([@bs.string] [ | `backPress | `hardwareBackPress], unit => bool) =>
+  EventSubscription.t =
   "";
 
 [@bs.scope "BackHandler"] [@bs.module "react-native"]

reason-react-native/src/apis/NetInfo.md

@@ -49,11 +49,9 @@ type info = {
   "effectiveType": EffectiveConnectionType.t,
 };
 
-type remove = {. "remove": unit => unit};
-
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
 external addEventListener:
-  ([@bs.string] [ | `connectionChange], info => unit) => remove =
+  ([@bs.string] [ | `connectionChange], info => unit) => EventSubscription.t =
   "";
 
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
@@ -70,7 +68,7 @@ external getConnectionInfo: unit => Js.Promise.t(info) = "";
 module IsConnected = {
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]
   external addEventListener:
-    ([@bs.string] [ | `connectionChange], bool => unit) => remove =
+    ([@bs.string] [ | `connectionChange], bool => unit) => EventSubscription.t =
     "";
 
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]

reason-react-native/src/apis/NetInfo.re

@@ -42,11 +42,9 @@ type info = {
   "effectiveType": EffectiveConnectionType.t,
 };
 
-type remove = {. "remove": unit => unit};
-
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
 external addEventListener:
-  ([@bs.string] [ | `connectionChange], info => unit) => remove =
+  ([@bs.string] [ | `connectionChange], info => unit) => EventSubscription.t =
   "";
 
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
@@ -63,7 +61,7 @@ external getConnectionInfo: unit => Js.Promise.t(info) = "";
 module IsConnected = {
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]
   external addEventListener:
-    ([@bs.string] [ | `connectionChange], bool => unit) => remove =
+    ([@bs.string] [ | `connectionChange], bool => unit) => EventSubscription.t =
     "";
 
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]

reason-react-native/src/apis/NetInfo.rei

@@ -42,11 +42,9 @@ type info = {
   "_type": ConnectionType.t,
 };
 
-type remove = {. "remove": unit => unit};
-
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
 external addEventListener:
-  ([@bs.string] [ | `connectionChange], info => unit) => remove =
+  ([@bs.string] [ | `connectionChange], info => unit) => EventSubscription.t =
   "";
 
 [@bs.module "react-native"] [@bs.scope "NetInfo"]
@@ -63,7 +61,7 @@ external getConnectionInfo: unit => Js.Promise.t(info) = "";
 module IsConnected: {
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]
   external addEventListener:
-    ([@bs.string] [ | `connectionChange], bool => unit) => remove =
+    ([@bs.string] [ | `connectionChange], bool => unit) => EventSubscription.t =
     "";
 
   [@bs.module "react-native"] [@bs.scope ("NetInfo", "isConnected")]