[ci] Remove unused jjbb variable

.ci/jobs.t/elastic+elasticsearch+periodic+bwc.yml

@@ -3,7 +3,6 @@ jjbb-template: matrix-gradle-unix-disabled.yml
 vars:
   - job-name: elastic+elasticsearch+%BRANCH%+periodic+bwc
   - job-display-name: "elastic / elasticsearch # %BRANCH% - backwards compatibility matrix"
-  - job-description: "Testing of the Elasticsearch %BRANCH% branch backwards compatibility matrix.\n"
   - matrix-yaml-file: ".ci/bwcVersions"
   - matrix-variable: BWC_VERSION
   - gradle-args: "-Dbwc.checkout.align=true v$BWC_VERSION#bwcTest"