RFR: 8331719: Cleanup asserts/code after introducing IsSTWGCActiveMark

[xiaotaonan]

On Mon, 13 May 2024 11:09:44 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> > This issue was assigned by @shipilev . Not know whether he had a patch locally. It may be good for him to have a look.
> 
> Actually, this was assigned to one of our folks. The common courtesy protocol is to _ask_ whether you can take the assignment off someone's hands. For many patches, there is a background that might only be known to current assignee, who might have done some further research into the issue.
> 
> For example here, I was planning to also deal with `G1CollectedHeap::do_collection_pause_at_safepoint`, which can be inlined better.

Sorry for that,I will close this PR.

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PR Comment: https://git.openjdk.org/jdk/pull/19208#issuecomment-2108953884