Move sample source and resources to gradle dirs

Summary: Follow standard Gradle paths.

Reviewed By: priteshrnandgaonkar

Differential Revision: D8890133

fbshipit-source-id: 062331b6b3d5f118f07cb5ca14cdec871f75867b

android/sample/build.gradle

@@ -16,12 +16,6 @@ android {
     sourceSets {
         main {
             manifest.srcFile './AndroidManifest.xml'
-            java {
-                srcDir 'src'
-            }
-            res {
-                srcDir 'res'
-            }
         }
     }
 }