Clean up dead code & outdated comment in app image validation

After I8f2a1ab1baa8f09e7a7d4913ff790927eb66cddf there was a stale
comment left around and code left around to extract the runtime
ClassLoader's dex file names.

Test: test/testrunner/testrunner.py -b --host
Change-Id: I8194f1188d23b59c90d0a10fbc14e53225ebce6a
3 files changed