RFR: 8298281: Serial: Refactor MarkAndPushClosure [v2]

[Albert Mingkun Yang]

> Simple change of removing some redundant code in oop-iteration.
> 
> 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/11562/files
  - new: https://git.openjdk.org/jdk/pull/11562/files/a9a5e789..a8b81166

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11562&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11562&range=00-01

  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11562.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11562/head:pull/11562

PR: https://git.openjdk.org/jdk/pull/11562