RFR: 8276921: G1: Remove redundant failed evacuation regions calculation in RemoveSelfForwardPtrHRClosure [v2]

[Hamlin Li]

> This is a minor optimization.
> We already have the number of failed evacuation region numbers, there is no need to calculate it on fly, at least in product code, so make it debug only, and add assert to verify the result.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Remove completely

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6362/files
  - new: https://git.openjdk.java.net/jdk/pull/6362/files/0637b050..7f0f14a7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6362&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6362&range=00-01

  Stats: 15 lines in 2 files changed: 0 ins; 13 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6362.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6362/head:pull/6362

PR: https://git.openjdk.java.net/jdk/pull/6362