[jdk21u-dev] RFR: 8316693: Simplify at-requires checkDockerSupport()

[Goetz Lindenmaier]

I backport this for parity with 21.0.3-oracle.

Checked that tests using @requires docker.support still work.

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Commit messages:
 - Backport 16fd43c5eb0fb18e93f00b5817d368df5afad969

Changes: https://git.openjdk.org/jdk21u-dev/pull/115/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=115&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316693
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/115.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/115/head:pull/115

PR: https://git.openjdk.org/jdk21u-dev/pull/115