Drop isolated_app auditallow rule.

This functionality is being used, apparently.

Addresses the following auditallow spam:

  type=1400 audit(0.0:1039): avc: granted { write } for
  comm="Chrome_ProcessL"
  path="/storage/emulated/0/Android/data/com.bleacherreport.android.teamstream/cache/.com.google.Chrome.sk5n91"
  dev="sdcardfs" ino=1877565 scontext=u:r:isolated_app:s0:c512,c768
  tcontext=u:object_r:sdcardfs:s0 tclass=file

Test: policy compiles.
Bug: 32896414
Change-Id: I627e20c38115f1d579e78ca12abfa717d32a155a