RFR: 8280136: Serial: Remove unnecessary use of ExpandHeap_lock [v5]

[Albert Mingkun Yang]

On Tue, 15 Feb 2022 10:09:55 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> This PR consists of two commits:
>> 
>> 1. remove `ExpandHeap_lock` in Serial GC code.
>> 2. rename it to `ParallelExpandHeap_lock` to indicate it's Parallel-GC only.
>> 
>> Test: tier1-6
>
> Albert Mingkun Yang has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - rename
>  - revert review

Thanks for the review.

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PR: https://git.openjdk.java.net/jdk/pull/7124