RFR: 8290459: Remove unused GCCause enums

[Axel Boldt-Christmas]

8290459: Remove unused GCCause enums

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Commit messages:
 - Merge branch 'JDK-8290459' of github.com:xmas92/jdk into JDK-8290459
 - Remove unused GCCause enums
 - Remove unused GCCause enums

Changes: https://git.openjdk.org/jdk/pull/9614/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9614&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290459
  Stats: 19 lines in 2 files changed: 0 ins; 18 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9614.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9614/head:pull/9614

PR: https://git.openjdk.org/jdk/pull/9614