RFR: 8280374: G1: Remove unnecessary prev bitmap mark

[Hamlin Li]

In JDK-8278917, the prev bitmap is used to mark evac failure objs, so at the post of evacuation, the evacuation failure objects are already marked during pss evacuation, so there is no need to mark them again in remove self forwardee phase.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/7153/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7153&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280374
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7153.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7153/head:pull/7153

PR: https://git.openjdk.java.net/jdk/pull/7153