RFR: 8277824: Remove empty RefProcSubPhasesWorkerTimeTracker destructor

[Albert Mingkun Yang]

Simple change removing effectively dead code, and some general cleanup.

Test: hotspot_gc

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Commit messages:
 - rp-time-tracker

Changes: https://git.openjdk.java.net/jdk/pull/6555/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6555&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277824
  Stats: 6 lines in 2 files changed: 0 ins; 4 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6555.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6555/head:pull/6555

PR: https://git.openjdk.java.net/jdk/pull/6555