Refactor runtime hidden API flag from negative to positive

There are only two situations in which we want to enable hidden API
access flag checks. Turning the flag from DISABLE_ to ENABLE_
simplifies logic in ART and reduces the number places where the flag
had to be passed down to ART.

Bug: 64382372
Test: boot device, install and run apps, check log messages
Change-Id: Ic5a531834360b614fc93d54221c7395579791184