ci: remove now useless OPENEDX_RELEASE variable

Author: regisb

.gitlab-ci.yml

@@ -2,7 +2,6 @@ variables:
     TUTOR_PLUGIN: mfe
     TUTOR_IMAGES: mfe authn-dev account-dev communications-dev course-authoring-dev discussions-dev gradebook-dev learner-dashboard-dev learning-dev ora-grading-dev profile-dev
     TUTOR_PYPI_PACKAGE: tutor-mfe
-    OPENEDX_RELEASE: palm
     GITHUB_REPO: overhangio/tutor-mfe
 
 include: