RFR: 8285851: Cleanup C2AtomicParseAccess::needs_pinning()

[Aleksey Shipilev]

It returns `true` by default, and the setter for it was removed by [JDK-8235653](https://bugs.openjdk.java.net/browse/JDK-8235653).

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/8455/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8455&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285851
  Stats: 7 lines in 2 files changed: 0 ins; 6 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8455.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8455/head:pull/8455

PR: https://git.openjdk.java.net/jdk/pull/8455