RFR: 8252695: Shenandoah: clean up Graal enabled/disabled filter in tests

[Aleksey Shipilev]

Drop `!vm.graal.enabled` since it is not required after JDK-8249000.

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Commit messages:
 - JDK-8252695

Changes: https://git.openjdk.java.net/jdk/pull/51/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=51&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252695
  Stats: 51 lines in 13 files changed: 0 ins; 0 del; 51 mod
  Patch: https://git.openjdk.java.net/jdk/pull/51.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/51/head:pull/51

PR: https://git.openjdk.java.net/jdk/pull/51