[localauth] Rename file

Author: Emmanuel Garcia

packages/local_auth/example/android/app/src/androidTest/java/io/flutter/plugins/localauth/MainActivityTest.java renamed to packages/local_auth/example/android/app/src/androidTest/java/io/flutter/plugins/localauth/FlutterFragmentActivityTest.java

@@ -7,7 +7,7 @@
 import org.junit.runner.RunWith;
 
 @RunWith(FlutterTestRunner.class)
-public class FlutterFragmentActivityTest {
+public class MainActivityTest {
   @Rule
   public ActivityTestRule<FlutterFragmentActivity> rule =
       new ActivityTestRule<>(FlutterFragmentActivity.class);