RFR: 8311086: Remove jtreg/gc/startup_warnings

[Hamlin Li]

On Thu, 29 Jun 2023 12:14:50 GMT, Leo Korinth <lkorinth at openjdk.org> wrote:

> It does not seem important to check that certain GCs are not deprecated.
> 
> The test originally tested that we created deprecation warnings on features that are now removed. What is left is not worth having IMO.

Marked as reviewed by mli (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/14709#pullrequestreview-1506607395