android: simplify using the Google Maven repo reference

Also remove mavenLocal since we don't need it.

android/build.gradle

@@ -3,8 +3,8 @@
 
 buildscript {
     repositories {
+        google()
         jcenter()
-        maven { url 'https://maven.google.com' }
     }
     dependencies {
         classpath 'com.android.tools.build:gradle:3.0.0'
@@ -16,9 +16,8 @@ buildscript {
 
 allprojects {
     repositories {
-        mavenLocal()
+        google()
         jcenter()
-        maven { url "https://maven.google.com" } // Required for appcompat.
         // React Native (JS, Obj-C sources, Android binaries) is installed from
         // npm.
         maven { url "$rootDir/../node_modules/react-native/android" }