Return the right value in VerifyClass.

We used to return kNoFailure when a class was already processed.
But it could have had soft failures.

Also remove IsCompileTimeVerified to avoid future confusions and
introduce ShouldVerifyAtRuntime.

Add some more checks to make sure we record the right things in
the vdex file.

bug: 33845394
test: verifier_deps_test test-art-host
Change-Id: Iff11a96e825c85db416083413761981515f405b7