Removes stack trace from invalid behavior logging

In practice, this log is never triggered except during tests, where it
is always triggered. This results in noisy logging for tests. Since the
stack trace is never practically useful here, this change removes it
from the log.

Test: atest AssistHandleBehaviorControllerTest
BUG:141488179
Change-Id: Ib6b7198ff2e6a52990fc24ffff6c828e03d33c6a
FIX:141488179