RFR: 8267653: Remove Mutex::_safepoint_check_sometimes [v2]

[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).

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Add assert that the thread is terminated before taking Heap_lock

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4184/files
  - new: https://git.openjdk.java.net/jdk/pull/4184/files/d7f55efe..3dc9b3b9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4184&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4184&range=00-01

  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 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