RFR: 7796: Remove workflow status indicator in the readme

[Marcus Hirt]

Since running workflows in the context of main repo is no longer supported.

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Commit messages:
 - 7796: Remove workflow status indicator in the readme

Changes: https://git.openjdk.java.net/jmc/pull/399/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=399&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-7796
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jmc/pull/399.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/399/head:pull/399

PR: https://git.openjdk.java.net/jmc/pull/399