Resolve "Clean code"

Closes #13 (closed)

android/app/src/main/kotlin/org/benoitharrault/memory/MainActivity.kt

-package org.benoitharrault.memory
-
-import androidx.annotation.NonNull;
-import io.flutter.embedding.android.FlutterActivity
-import io.flutter.embedding.engine.FlutterEngine
-import io.flutter.plugins.GeneratedPluginRegistrant
-
-class MainActivity: FlutterActivity() {
-    override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
-        GeneratedPluginRegistrant.registerWith(flutterEngine);
-    }
-}