RFR: 7902991: fix deprecation warnings generated when compiling with JDK 16. [v2]

[Sergei Ustimenko]

On Thu, 8 Jul 2021 03:30:08 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> Sergei Ustimenko has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update copyrights
>
> I created a JBS issue, https://bugs.openjdk.java.net/browse/CODETOOLS-7902991
> The change looks OK, but note that the default build platform within Oracle is still JDK 8 and so the code must remain compilable by JDK 8 or with `--release 8`.

@jonathan-gibbons thanks for taking a look and helping me out with issue creation! I agree, I hoped this change would be helpful to reduce future efforts moving jtreg to newer versions.

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PR: https://git.openjdk.java.net/jtreg/pull/15