RFR: 8330960: Serial: Remove SerialFullGC::_total_invocations

[Guoxiong Li]

Hi all,

This patch removes the field `SerialFullGC::_total_invocations` and its related usages, and uses `CollectedHeap::_total_full_collections` instead.

Thanks for taking the time to review.

Best Regards,
-- Guoxiong

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Commit messages:
 - JDK-8330960

Changes: https://git.openjdk.org/jdk/pull/18930/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18930&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330960
  Stats: 12 lines in 2 files changed: 0 ins; 11 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18930.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18930/head:pull/18930

PR: https://git.openjdk.org/jdk/pull/18930