Make Trusted Hotword session permissions follow previous behavior

A prior change to the permissions flow for Trusted Hotword
(I80dabaf6ae0e781028dde16ead3321fbff319542) made the system enforce
the required permissions on the APIs the conventional way - by throwing
a SecurityException. But the existing behavior was to silence these
exceptions and instead return error results. This change brings back
the old behavior which exists in the SoundTrigger layer.

Also removes permissions checks for a couple of APIs to again be
consistent with the old behavior (and the current behavior in the
SoundTrigger layer).

Fix: 193116894
Test: manual - remove permission and reboot / remove permission after
 boot, stop/start reco
Test: atest HotwordDetectionServiceBasicTest
Change-Id: I56391260fd4375a04233eb3261bacec8696bda99