RFR: 8271939: Clean up primitive raw accessors in oopDesc

[Roman Kennke]

We have some _raw accessors in oop.hpp and related code. Those are leftover from when Shenandoah required primitive barriers and are no longer needed. Their uses can be replaced with the regular accessors.

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

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Commit messages:
 - 8271939: Clean up primitive raw accessors in oopDesc

Changes: https://git.openjdk.java.net/jdk/pull/5017/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5017&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271939
  Stats: 37 lines in 8 files changed: 0 ins; 30 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5017.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5017/head:pull/5017

PR: https://git.openjdk.java.net/jdk/pull/5017