ref(android) remove unused code

This basically reverts
e61ccc956f
since we are no longer interested in using Detox.

In addition, the WebRTC initialization code was only placed in the RAN
instance manager holder's App initialization path, which is now gone, so
add it to the Activity initialization path.

android/app/src/main/java/org/jitsi/meet/MainApplication.java

@@ -1,47 +0,0 @@
-/*
- * Copyright @ 2022-present 8x8, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jitsi.meet;
-
-import android.app.Application;
-import android.util.Log;
-
-import com.facebook.react.ReactApplication;
-import com.facebook.react.ReactNativeHost;
-
-import org.jitsi.meet.sdk.JitsiReactNativeHost;
-
-/**
- * Application class for Jitsi Meet. The only reason why this exists is for Detox
- * to believe our app is a "greenfield" app. SDK users need not use this.
- */
-public class MainApplication extends Application implements ReactApplication {
-    private final ReactNativeHost mReactNativeHost = new JitsiReactNativeHost(this);
-
-    @Override
-    public ReactNativeHost getReactNativeHost() {
-        return mReactNativeHost;
-    }
-
-    @Override
-    public void onCreate() {
-        super.onCreate();
-
-        // Initialize RN
-        Log.d(this.getClass().getCanonicalName(), "app onCreate");
-        getReactNativeHost().getReactInstanceManager();
-    }
-}