Fixed wrong field override breaking options menu in PreviewMediaFragment and PreviewImageFragment

src/com/owncloud/android/ui/preview/PreviewImageFragment.java

@@ -78,8 +78,6 @@ ConfirmationDialogFragment.ConfirmationDialogFragmentListener {
 
     private boolean mIgnoreFirstSavedState;
 
-    private FileFragment.ContainerActivity mContainerActivity;
-
     
     /**
      * Creates a fragment to preview an image.

src/com/owncloud/android/ui/preview/PreviewMediaFragment.java

@@ -90,8 +90,6 @@ public class PreviewMediaFragment extends FileFragment implements
     private boolean mAutoplay;
     public boolean mPrepared;
     
-    private FileFragment.ContainerActivity mContainerActivity;
-
     private static final String TAG = PreviewMediaFragment.class.getSimpleName();