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

[Albert Mingkun Yang]

On Fri, 12 Nov 2021 02:00:57 GMT, Hamlin Li <mli at openjdk.org> wrote:

> 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.

I think `_num_failed_regions` can be dropped completely; it's used for verification only. `~RemoveSelfForwardPtrsTask` can go as well as a cascading effect.

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