Remove stopship workaround for instant app targetSdkVersion

Instant Apps will need to target O and the v2 security sandbox. Replace
the hack that silently upgrades them with an error.
Test: cts-tradefed run commandAndExit cts-dev -m
CtsAppSecurityHostTestCases -t android.appsecurity.cts.EphemeralTest
Fixes: 62444631

Change-Id: If28602924f38c78c06a23efb7e28c8f17528c4cf