ADBRootService: Remove redundant permission check

 * First of all, the check is performed in a helper class, one can
   easily bypass it by directly issuing the binder API.
 * On the other hand, enforceCallingOrSelfPermission allows root and
   system UID to do everything, i.e., any process running in system UID
   is allowed to pass the check, including Settings app, thus it's
   simply a no-op.

Change-Id: I82f58d6165c2ef35c61047d5899de3e8ca6f7f39