RFR: 8272165: Consolidate mark_must_be_preserved() variants

[Roman Kennke]

We have markWord::mark_must_be_preserved() and markWord::mark_must_be_preserved_for_promotion_failure(). We used to have slightly different implementations when we had BiasedLocking, but now they are identical and used for identical purposes too. Let's remove what we don't need.

Testing:
 - [ ] hotspot_gc
 - [ ] tier1
 - [ ] tier2

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Commit messages:
 - 8272165: Consolidate mark_must_be_preserved() variants

Changes: https://git.openjdk.java.net/jdk/pull/5057/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5057&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272165
  Stats: 12 lines in 4 files changed: 0 ins; 11 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5057.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5057/head:pull/5057

PR: https://git.openjdk.java.net/jdk/pull/5057