RFR: 8253219: Epsilon: clean up unnecessary includes

[Thomas Schatzl]

On Wed, 16 Sep 2020 07:43:31 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Static analysis shows a few #include statements in gc/epsilon that are not needed.
> 
> Testing: Linux x86_64 {release, fastdebug, slowdebug} x {+PCH, -PCH}

Marked as reviewed by tschatzl (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/198