RFR: 8252871: fatal error: must own lock JvmtiThreadState_lock

[Robbin Ehn]

When these two methods (set_frame_pop/clear_frame_pop) are called in a handshake the requesting thread will have lock
the JvmtiThreadState_lock. But the thread executing one of these in the handshake may not be the owner.
So we only check that JvmtiThreadState_lock is locked.

When verifying the callers to these methods I notice "clear_to_frame_pop" was unused, so instead of fixing it I remove
it.

Passes testing locally, still running T3 and T7.

Now passed!

-------------

Commit messages:
 - Fix assert and removed unsed methods

Changes: https://git.openjdk.java.net/jdk/pull/60/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=60&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252871
  Stats: 26 lines in 4 files changed: 0 ins; 24 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/60.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/60/head:pull/60

PR: https://git.openjdk.java.net/jdk/pull/60