android: Drop LayerView.mContext

It's only assigned in the ctor, but never used later.

Change-Id: Ie7876c8eb4f22cd03f1e3743950e402b51c67db1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/194198
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Tested-by: Jenkins

android/source/src/java/org/mozilla/gecko/gfx/LayerView.java

@@ -47,11 +47,9 @@ public class LayerView extends FrameLayout {
     private final SurfaceView mSurfaceView;
 
     private Listener mListener;
-    private final LibreOfficeMainActivity mContext;
 
     public LayerView(Context context, AttributeSet attrs) {
         super(context, attrs);
-        mContext = (LibreOfficeMainActivity) context;
 
         mSurfaceView = new SurfaceView(context);
         addView(mSurfaceView, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);