RFR: 8267653: Remove Mutex::_safepoint_check_sometimes

[Coleen Phillimore]

Since SR_lock is removed, this state of declaring locks as sometimes safepoint checking and not is no longer used.  JavaThreads either always or never check for safepoint, depending on the lock.  The Heap_lock was always a bit special because it's taken by a JavaThread after it exits, but the code in mutex::lock_contended already deals with this (ie doesn't safepoint check while exiting).
Tested with tier 2-3 and tier1 in progress.
Thanks to Zhengu for testing and confirming shenandoah (I built and ran shenandoah tests too).

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Commit messages:
 - 8267653: Remove Mutex::_safepoint_check_sometimes

Changes: https://git.openjdk.java.net/jdk/pull/4184/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4184&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267653
  Stats: 22 lines in 5 files changed: 0 ins; 19 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4184.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4184/head:pull/4184

PR: https://git.openjdk.java.net/jdk/pull/4184