Change well known thread methods to `ArtMethod*`.

Also rename `java_lang_ThreadGroup_removeThread` to
`java_lang_ThreadGroup_threadTerminated` in line with
the actual method it references.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: Iaf2644d006f44759a47587c82db2dcdba0bfa67e
20 files changed