[14] RFR 8240217: Shenandoah: remove ShenandoahEvacAssist

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8240217
  https://hg.openjdk.java.net/jdk/jdk/rev/c005ba590219

14u fix does not apply cleanly due to context changes. This is not a big deal, because the conflict
is in the hunk that removes the entire piece of code. 14u webrev:
  https://cr.openjdk.java.net/~shade/8240217/webrev.14u.01/

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey