ART: Skip compiler-driver compile loop for VerifyAtRuntime

We don't compile (not even dex-to-dex) anyways, so skip iterating
over all methods. Shows a ~10% improvement of boot image compile
time on Nexus 9. Shows a ~40% improvement for a common large app
on the same device. Most of the remaining time is unzipping dex
files.

Bug: 24103765
Change-Id: I00931fd062a0a2297d1c7b90794302cb664571cc