Clean up launched mediaProjectionKeyguardRestrictions flag

Fix the MP unit tests:
 - There's a duplicate one in StopControllerTest and ServiceTest
 - It doesn't need to properly acquire the role, a mock that the
   role is held is enough

#codehealth

Bug: 348335290
Test: presubmit
Flag: EXEMPT cleanup
Change-Id: I350f50164cb7843bcdd36693f0c0f99e3a31869c