RFR: CODETOOLS-7903303: remove local copy of RuntimeVersion [v2]

[Jonathan Gibbons]

> Please review an almost trivial change, to use the standard `Runtime.Version` class now that `jtreg` assumes JDK >= 11, and to remove the local "cached" copy in `RuntimeVersion`.

Jonathan Gibbons has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/master' into jtreg.7903303.runtime-version
 - CODETOOLS-7903303: remove local copy of RuntimeVersion

-------------

Changes:
  - all: https://git.openjdk.org/jtreg/pull/119/files
  - new: https://git.openjdk.org/jtreg/pull/119/files/567ef5c7..adcff893

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jtreg&pr=119&range=01
 - incr: https://webrevs.openjdk.org/?repo=jtreg&pr=119&range=00-01

  Stats: 1043 lines in 20 files changed: 800 ins; 191 del; 52 mod
  Patch: https://git.openjdk.org/jtreg/pull/119.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/119/head:pull/119

PR: https://git.openjdk.org/jtreg/pull/119