RFR: 8277560: Remove WorkerDataArray::_is_serial [v2]

[Albert Mingkun Yang]

> Simple change of removing effectively dead code.
> 
> Test: build

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.java.net/jdk/pull/6502/files
  - new: https://git.openjdk.java.net/jdk/pull/6502/files/7138fb8d..14926d2f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6502&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6502&range=00-01

  Stats: 12 lines in 2 files changed: 0 ins; 12 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6502.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6502/head:pull/6502

PR: https://git.openjdk.java.net/jdk/pull/6502