RFR: 8272216: G1: replace G1ParScanThreadState::_dest with a constant

[Albert Mingkun Yang]

Simple change of removing an array with statically-known identical elements.

Test: hotspot_gc

-------------

Commit messages:
 - dest

Changes: https://git.openjdk.java.net/jdk/pull/5065/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5065&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272216
  Stats: 17 lines in 2 files changed: 2 ins; 14 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5065.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5065/head:pull/5065

PR: https://git.openjdk.java.net/jdk/pull/5065