Allow holders of WRITE_MEDIA_STORAGE to write to secondary external storage

Apps with WRITE_MEDIA_STORAGE can write to the secondary
external storage directly so there is no need to prevent
that through the MediaProvider.

Change-Id: If092fcdf0b90599afdb52a8e6ae4c7ba1090acc4

Conflicts:
	src/com/android/providers/media/MediaProvider.java