Deprecate WRITE_MEDIA_STORAGE permission

Previously, this permission would give the holder the media_rw gid
thereby granting access to the following file paths on disk:
1. /data/media
2. /mnt/media_rw
3. /mnt/expand/<uuid>/data/media

With the introduction of a stacked FUSE filesystem on external
storage, modifying any files directly on the lower filesystem (the
paths listed above) could lead to VFS cache inconsistencies and file
corruption.

To mitigate this risk, this cl blocks unneeded access to the lower
filesystem. Apps relying on this permission should instead use
android.permission.MANAGE_EXTERNAL_STORAGE.

Test: cat /proc/<pid>/status of mediaprovider doesn't have media_rw
Bug: 144914977

Change-Id: I8335d18067231657ac9793f7b1dcf6adb617ecfc