RFR: 8301465: Remove unnecessary nmethod arming in Full GC of Serial/Parallel [v2]

[Albert Mingkun Yang]

> Simple removing unnecessary code and adding API documentation.
> 
> Test: hotspot_gc

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12311/files
  - new: https://git.openjdk.org/jdk/pull/12311/files/49ac215a..c78f41b6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12311&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12311&range=00-01

  Stats: 13 lines in 2 files changed: 7 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12311.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12311/head:pull/12311

PR: https://git.openjdk.org/jdk/pull/12311