[14] RFR 8242400: Shenandoah: Restore logging to pre-jdk8241984 format

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8242400
  https://hg.openjdk.java.net/jdk/jdk/rev/7992ff451fec

Missing GCTraceConcTimeImpl -> GCTraceConcTime rename in 14u yields the conflict. Trivially resolved
by changing it back.

14u webrev:
  https://cr.openjdk.java.net/~shade/8242400/webrev.14u.01/

Testing: hotspot_gc_shenandoah {fastdebug,release}, tier{1,2} with Shenandoah

-- 
Thanks,
-Aleksey