Don't allow package verifier to be disabled via Settings.

We no longer allow a global setting to prevent the package verifier
from being invoked for a non-adb install. The verifier itself may
still check the setting, or have its own controls, but it always gets
a chance to run.

Test: atest PackageVerifierTest
Bug: 135751498
Change-Id: I31a6571f86bae89c5147e91609355610aebfacc6