RFR (XS) 8240216: Shenandoah: remove ShenandoahTerminationTrace

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8240216

This was the diagnostic option for working on improving the termination protocol. Now that VM had
moved globally to OWST as termination protocol, this seems to only increase the maintenance burden.
The option is turned off by default already.

Zhengyu, do you agree?

Webrev:
  https://cr.openjdk.java.net/~shade/8240216/webrev.01/

Testing: hotspot_gc_shenandoah {fastdebug,release}

-- 
Thanks,
-Aleksey