RFR: Remove fix-roots pass in ShHeap

[Roman Kennke]

We have an extra fix-roots pass in ShHeap that is supposed to fix up any
roots after cancelled init-evac pass. This is a cludge that predates the
evac-oom-handler. Now that we have a reliable evac-oom-handler, this
would take care of that. We can remove that pass.

Testing: tier3_gc_shenandoah ok

http://cr.openjdk.java.net/~rkennke/remove-fixroots/webrev.00/

Ok?

Roman