Remove leftover PR link for previously disabled bwc tests

build.gradle

@@ -145,7 +145,7 @@ task verifyVersions {
  * after the backport of the backcompat code is complete.
  */
 final boolean bwc_tests_enabled = true
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/28673" /* place a PR link here when commiting bwc changes */
+final String bwc_tests_disabled_issue = "" /* place a PR link here when commiting bwc changes */
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {
     throw new GradleException("bwc_tests_disabled_issue must be set when bwc_tests_enabled == false")