Removing Google Play services requirement. (#361)

Firebase Android SDKs for Auth, Database, Storage, Functions do not require Google Play Services anymore.
https://firebase.google.com/docs/android/android-play-services

Removing checks for Google Play services for these products from the C++ SDK. 
Tested by running integration tests on, 
- devices with Google play services (https://github.com/firebase/firebase-cpp-sdk/actions/runs/730345555)
- devices without Google Play services (tested on Kindle)
- android emulator images with and without google play services. 

Addresses firebase/quickstart-unity#975

Author: vimanyu

auth/src/auth.cc

@@ -46,7 +46,6 @@
 FIREBASE_APP_REGISTER_CALLBACKS(
     auth,
     {
-      FIREBASE_UTIL_RETURN_FAILURE_IF_GOOGLE_PLAY_UNAVAILABLE(*app);
       return ::firebase::kInitResultSuccess;
     },
     {
@@ -75,8 +74,6 @@ Auth* Auth::GetAuth(App* app, InitResult* init_result_out) {
     return existing_auth;
   }
 
-  FIREBASE_UTIL_RETURN_NULL_IF_GOOGLE_PLAY_UNAVAILABLE(*app, init_result_out);
-
   // Create the platform dependent version of Auth.
   void* auth_impl = CreatePlatformAuth(app);
   if (!auth_impl) return nullptr;

database/src/common/database.cc

@@ -43,7 +43,6 @@
 FIREBASE_APP_REGISTER_CALLBACKS(
     database,
     {
-      FIREBASE_UTIL_RETURN_FAILURE_IF_GOOGLE_PLAY_UNAVAILABLE(*app);
       return ::firebase::kInitResultSuccess;
     },
     {
@@ -84,7 +83,6 @@ Database* Database::GetInstance(App* app, const char* url,
     if (init_result_out != nullptr) *init_result_out = kInitResultSuccess;
     return it->second;
   }
-  FIREBASE_UTIL_RETURN_NULL_IF_GOOGLE_PLAY_UNAVAILABLE(*app, init_result_out);
 
   Database* database = url ? new Database(app, new DatabaseInternal(app, url))
                            : new Database(app, new DatabaseInternal(app));

functions/src/common/functions.cc

@@ -40,7 +40,6 @@
 FIREBASE_APP_REGISTER_CALLBACKS(
     functions,
     {
-      FIREBASE_UTIL_RETURN_FAILURE_IF_GOOGLE_PLAY_UNAVAILABLE(*app);
       return ::firebase::kInitResultSuccess;
     },
     {
@@ -84,7 +83,6 @@ Functions* Functions::GetInstance(::firebase::App* app, const char* region,
     if (init_result_out != nullptr) *init_result_out = kInitResultSuccess;
     return it->second;
   }
-  FIREBASE_UTIL_RETURN_NULL_IF_GOOGLE_PLAY_UNAVAILABLE(*app, init_result_out);
 
   Functions* functions = new Functions(app, region_idx.c_str());
   if (!functions->internal_->initialized()) {

release_build_files/readme.md

@@ -587,6 +587,9 @@ code.
     -   General: Fixed rare crashes at application exit when destructors were
         being executed
         ([#345](https://github.com/firebase/firebase-cpp-sdk/pull/345)).
+    -   General (Android): Removed checks for Google Play services for Auth, Database,
+        Functions and Storage as the native Android packages no longer need it.
+        ([#361](https://github.com/firebase/firebase-cpp-sdk/pull/361)).
 
 ### 7.1.1
 -   Changes

storage/src/common/storage.cc

@@ -41,7 +41,6 @@
 FIREBASE_APP_REGISTER_CALLBACKS(
     storage,
     {
-      FIREBASE_UTIL_RETURN_FAILURE_IF_GOOGLE_PLAY_UNAVAILABLE(*app);
       return ::firebase::kInitResultSuccess;
     },
     {
@@ -103,7 +102,6 @@ Storage* Storage::GetInstance(::firebase::App* app, const char* url,
     if (init_result_out != nullptr) *init_result_out = kInitResultSuccess;
     return it->second;
   }
-  FIREBASE_UTIL_RETURN_NULL_IF_GOOGLE_PLAY_UNAVAILABLE(*app, init_result_out);
 
   Storage* storage = new Storage(app, url);
   if (!storage->internal_->initialized()) {