RFR: 8234532: Remove ThreadLocalAllocBuffer::_fast_refill_waste since it is never set [v3]

[Per Liden]

On Thu, 29 Apr 2021 08:11:12 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> It has some cascading effect; two performance variables, `fastWaste` and `maxFastWaste`, can be removed also.
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

Looks good.

But we should also probably rename `_slow_refill_waste` to `_refill_waste`, since "slow" doesn't really make sense anymore. Of course, that would also affect the `slowWaste` PerfCounter. Maybe this could be a follow up refinement?

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Marked as reviewed by pliden (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3756