RFR: 8260586: Shenandoah: simplify "Concurrent Weak References" logging

[Aleksey Shipilev]

Concurrent Weak References always does parallel worker operation. Therefore "Process" counter is redundant, and we might as well make the root counter the per-worker one. This simplifies GC logging.

Old log:

[95.220s][info][gc,stats] Concurrent Weak References         1709 us
[95.220s][info][gc,stats]   Process                          1588 us, parallelism: 1.30x
[95.220s][info][gc,stats]     CWRF: <total>                  2056 us
[95.220s][info][gc,stats]     CWRF: Weak References          2056 us, workers (us): 454, 1450,   2, 145,   4,   1,   0,   0, 

New log:

[39.583s][info][gc,stats] Concurrent Weak References          651 us, parallelism: 1.52x
[39.583s][info][gc,stats]   CWRF: <total>                     986 us
[39.583s][info][gc,stats]   CWRF: Weak References             986 us, workers (us): 183,  29, 145, 627,   1,   0,   0,   0,

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

Commit messages:
 - 8260586: Shenandoah: simplify "Concurrent Weak References" logging

Changes: https://git.openjdk.java.net/jdk/pull/2288/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2288&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260586
  Stats: 6 lines in 3 files changed: 0 ins; 2 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2288.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2288/head:pull/2288

PR: https://git.openjdk.java.net/jdk/pull/2288