RFR: 8273929: Remove GzipRandomAccess in heap dump test

[Lin Zang]

On Fri, 17 Sep 2021 08:24:54 GMT, Lin Zang <lzang at openjdk.org> wrote:

> The class `GzipRandomAccess` is used to parse heap dump file generated from `jcmd`/`jmap` tools when testing.
> It has the limitation that only gzip file which has "blocksize" header field could be sucessfully parsed.
> We think this class can be removed for 2 reasons:
> 1. The gzip heap dump file generated by `jhsdb` command does not contain the "blocksize" header field, so the GzipRandomAccess can not parse the generated file successfully.
> 2. The `GzipInputStream` could be used instead and then gziped heap dump file generated from both `jcmd`/`jmap` and `jhsdb jmap` could be parsed using same logic.
> Options

Dear Chris @plummercj, 
May I ask your help to take look at this again? Do you think my expaination about "use of decompressed file" is OK? 
Thanks!
Lin

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PR: https://git.openjdk.java.net/jdk/pull/5556