RFR: BrooksPointer tracing overwhelms -Xlog:gc=trace

[Aleksey Shipilev]

Zhengyu had recently added the test that exercises different log levels. Sometimes, e.g. when that
test is falling into Full GC, the logs are overwhelmed with messages like these:

[2427.622s][trace][gc] GC(1) Forwardee for 0x00000006c3501360 = 0x00000006c3501360
[2427.622s][trace][gc] GC(1) Forwardee for 0x00000006c0039810 = 0x00000006c0039810

Logging every fwdptr operation is sure excessive, let's relax it:
 http://cr.openjdk.java.net/~shade/shenandoah/brooks-nolog/webrev.01/

Additionally, cleaned up unused methods and made sure we call Verifier on interesting paths.

Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey