Changes needed for gradle 3.0.1 compatibility

Some minor changes are needed for gradle 3.0.1 compatibility: in android/build.gradle:
* Remove the `buildToolsVersion`, gradle now specifies a default and the current value conflicts with that.
* Declare dependencies using `api` not `compile` per https://developer.android.com/studio/build/gradle-plugin-3-0-0-migration.html#new_configurations

We are currently hacking these changes with a script in status.im, and would rather it is fixed upstream. Thanks!

Parent issue: https://github.com/status-im/status-react/issues/3037

Using react-native version 0.51.0, react-native-fcm version 10.0.3 (but problem still exists in your latest version v11.3.0).