RFR: 8234020: Remove FullGCCount_lock

[Albert Mingkun Yang]

Remove an unused method and unnecessary synchronization in Serial GC.

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Commit messages:
 - fullgclock

Changes: https://git.openjdk.java.net/jdk/pull/3679/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3679&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234020
  Stats: 23 lines in 4 files changed: 0 ins; 23 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3679.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3679/head:pull/3679

PR: https://git.openjdk.java.net/jdk/pull/3679