Gallery2: force close happens on deleting MMS attachment

When open a MMS attached picture, zoom out and pull down,
force close happens for PhotoView doesn't support delete
single photo in SinglePhotoDataAdapter.

So we cut this delete function in SinglePhotoDataAdapter
to avoid NullPointerException in Gallery.

CRs-Fixed: 523924

Change-Id: I58baac9316cfbeba8509e118dd00c4f74d2a885c