Use ArtMethod::GetDexFile() instead of using declaring class.

This is a follow-up to
    https://android-review.googlesource.com/834082 .

Test: m test-art-host-gtest
Test: testrunner.py --host
Bug: 119830111
Change-Id: I5bd55b0293ef176385a7e9d8b296be6b470cfcc4
2 files changed