Android: Remove rxjava lib

No need to keep rxjava lib around for one simple use case

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/utils/Action1.java

@@ -0,0 +1,6 @@
+package org.dolphinemu.dolphinemu.utils;
+
+public interface Action1<T>
+{
+  void call(T t);
+}

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/utils/DirectoryStateReceiver.java

@@ -6,8 +6,6 @@ import android.content.Intent;
 
 import org.dolphinemu.dolphinemu.utils.DirectoryInitialization.DirectoryInitializationState;
 
-import rx.functions.Action1;
-
 public class DirectoryStateReceiver extends BroadcastReceiver
 {
   Action1<DirectoryInitializationState> callback;