Allow installd to delete files via sdcardfs.

When installd clears cached files on external storage, the sdcardfs
kernel filesystem needs to be kept in the loop to release any cached
dentries that it's holding onto.  (Otherwise the underlying disk
space isn't actually released.)

installd can already delete the underlying files directly (via the
media_rw_data_file rules), so this technically isn't expanding its
capabilities.

avc: granted { search } for name="/" dev="tmpfs" ino=6897 scontext=u:r:installd:s0 tcontext=u:object_r:tmpfs:s0 tclass=dir
avc: denied { open } for path="/mnt/runtime/default/emulated/0/Android/data" dev="sdcardfs" ino=589830 scontext=u:r:installd:s0 tcontext=u:object_r:sdcardfs:s0 tclass=dir permissive=1
avc: denied { write } for name="com.google.android.inputmethod.japanese" dev="sdcardfs" ino=590040 scontext=u:r:installd:s0 tcontext=u:object_r:sdcardfs:s0 tclass=dir permissive=0
avc: denied { remove_name } for name="cache_r.m" dev="sdcardfs" ino=589868 scontext=u:r:installd:s0 tcontext=u:object_r:sdcardfs:s0 tclass=dir permissive=0
avc: denied { getattr } for path="/mnt/runtime/default/emulated/0/Android/data/.nomedia" dev="sdcardfs" ino=589831 scontext=u:r:installd:s0 tcontext=u:object_r:sdcardfs:s0 tclass=file permissive=1

Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.StorageHostTest
Bug: 37486230
Change-Id: Icfd00a9ba379b1f50c48fe85849304cf9859bcb2
(cherry picked from commit 72f4c619)