[jdk16u] RFR: 8258534: Epsilon: clean up unused includes

[Aleksey Shipilev]

This simplifies the build and keeps codebases in sync.

Additional testing:
 - [x] Linux x86_64 fastdebug `gc/epsilon`
 - [x] Linux x86_64 release `gc/epsilon`

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Commit messages:
 - Backport 3817c32fd1dba46ff1ee1831aa5efb03c6546ace

Changes: https://git.openjdk.java.net/jdk16u/pull/65/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=65&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258534
  Stats: 2 lines in 2 files changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/65.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/65/head:pull/65

PR: https://git.openjdk.java.net/jdk16u/pull/65