Remove null check on the result of Class.forName.

The method never returns `null`; it either fails or returns the `Class`.

As a result, I am making calls like this into errors in google/error-prone#6093.

PiperOrigin-RevId: 989783886

Author: cpovirk

ext/junit/java/androidx/test/ext/junit/runners/AndroidJUnit4.java

@@ -71,7 +71,8 @@ && hasClass("org.robolectric.RobolectricTestRunner")) {
 
   private static boolean hasClass(String className) {
     try {
-      return Class.forName(className) != null;
+      Class<?> unused = Class.forName(className);
+      return true;
     } catch (ClassNotFoundException e) {
       return false;
     }