RFR: 8260584: Shenandoah: simplify "Concurrent Thread Roots" logging

[Aleksey Shipilev]

There are two separate counters now:

 f(conc_thread_roots, "Concurrent Stack Processing") \
 f(conc_thread_roots_work, " Threads") \
  SHENANDOAH_PAR_PHASE_DO(conc_thread_roots_work_, " CT: ", f) \
...and `_work` counter is unused, and `conc_thread_roots` is used to report worker stats. So the log says `<total>`, where `Thread Roots` should have been mentioned:

[34.169s][info][gc,stats] Concurrent Stack Processing       11341 us, parallelism: 7.93x
[34.169s][info][gc,stats]   Threads                         89908 us
[34.169s][info][gc,stats]     CT: <total>                   89908 us, workers (us): 11231, 11270, 11251, 11252, 11237, 11230, 11214, 11223, 

Fixed log says:

[99.797s][info][gc,stats] Concurrent Thread Roots            3929 us, parallelism: 7.45x
[99.797s][info][gc,stats]   CTR: <total>                    29273 us
[99.797s][info][gc,stats]   CTR: Thread Roots               29273 us, workers (us): 3652, 3643, 3622, 3623, 3623, 3676, 3606, 3829, 

Also, I believe it should be called "Concurrent Thread Roots", in symmetry with "Concurrent Update Thread Roots" later.

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Commit messages:
 - 8260584: Shenandoah: simplify "Concurrent Thread Roots" logging

Changes: https://git.openjdk.java.net/jdk/pull/2287/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2287&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260584
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2287.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2287/head:pull/2287

PR: https://git.openjdk.java.net/jdk/pull/2287