priv_app.te: refine cache_recovery_file auditallow rules

priv_app reads from /cache/recovery, but I'm still not sure if
it writes. Eliminate the read auditallow rules and allow the
writes to show up (if any).

Eliminates the following auditallow messages:

  avc: granted { search } for comm="IntentService[S" name="recovery" dev="mmcblk0p38" ino=12 scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:cache_recovery_file:s0 tclass=dir
  avc: granted { getattr } for comm="Thread-1" path="/cache/recovery/last_install" dev="mmcblk0p27" ino=29891 scontext=u:r:priv_app:s0:c525,c768 tcontext=u:object_r:cache_recovery_file:s0 tclass=file
  avc: granted { read open } for comm="Thread-1" name="recovery" dev="mmcblk0p27" ino=29889 scontext=u:r:priv_app:s0:c525,c768 tcontext=u:object_r:cache_recovery_file:s0 tclass=dir

Change-Id: Ibc0640f5366aae50e3fd09d17657374390b24a5c