Remove unnecessary configs from RNTester

Summary:
This is a nit cleanup of RNTester's build.gradle.

1. We should not create new configurations such as `hermesDebugImplementation` as those are automatically created by AGP.
2. We should not add imports of external .jar as we don't have them (and this generates a warning on console).

Changelog:
[Internal] [Changed] - Remove unnecessary configs from RNTester

Created from CodeHub with https://fburl.com/edit-in-codehub

Reviewed By: cipolleschi

Differential Revision: D38737330

fbshipit-source-id: e23f234f68c839af065d4948af6c780186cbdf3d

packages/rn-tester/android/app/build.gradle

@@ -197,14 +197,7 @@ android {
     }
 }
 
-configurations {
-  hermesDebugImplementation {}
-  hermesReleaseImplementation {}
-}
-
 dependencies {
-    implementation fileTree(dir: 'libs', include: ['*.jar'])
-
     // Build React Native from source
     implementation project(':ReactAndroid')