fix(android): drop library targetSdk for AGP 9 (#1549)

## Description

- Drop library `targetSdk`: AGP 9 (RN 0.88) removed it, so
`build.gradle.kts` fails to compile. It never affected the app.

### Introduces a breaking change?

- [ ] Yes
- [x] No

### Type of change

- [x] Bug fix (change which fixes an issue)
- [ ] New feature (change which adds functionality)
- [ ] Documentation update (improves or adds clarity to existing
documentation)
- [ ] Other (chores, tests, code style improvements etc.)

### Tested on

- [ ] iOS
- [x] Android

### Testing instructions

- Fresh RN 0.88.0 app: `main` fails with `Unresolved reference
'targetSdk'`; this builds and runs a text embedding model on device.

### Screenshots

### Related issues

#1547

### Checklist

- [x] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [x] My changes generate no new warnings

### Additional notes

Author: msluszniak

packages/react-native-executorch-webrtc/android/build.gradle

@@ -31,7 +31,6 @@ android {
 
     defaultConfig {
         minSdkVersion 26
-        targetSdkVersion 34
 
         externalNativeBuild {
             cmake {

packages/react-native-executorch/android/build.gradle.kts

@@ -116,7 +116,6 @@ android {
         // ships a library its linker is not guaranteed to be able to load. The
         // default was 21, which let such a build through to fail on the device.
         minSdk = (getExtOrDefault("minSdkVersion", 26) as Number).toInt()
-        targetSdk = (getExtOrDefault("targetSdkVersion", 34) as Number).toInt()
         consumerProguardFiles("consumer-proguard-rules.pro")
 
         externalNativeBuild {