RFR: 7256: Use .jcheck/conf property to control version

[Marcus Hirt]

See Erik Joelsson's comment in https://bugs.openjdk.java.net/browse/SKARA-1033.

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

Commit messages:
 - 7256: Use .jcheck/conf property to control version
 - Merge branch 'master' into 7046-update-2021-03
 - Removing chromium
 - 7046: Update to the 2021-03 platform

Changes: https://git.openjdk.java.net/jmc/pull/249/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=249&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7256
  Stats: 109 lines in 7 files changed: 90 ins; 3 del; 16 mod
  Patch: https://git.openjdk.java.net/jmc/pull/249.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/249/head:pull/249

PR: https://git.openjdk.java.net/jmc/pull/249