ci: Drop check-merge-request job

The job is broken due to permission changes in GitLab, and it seems what
is checked for is now the default, making the job less useful, thus drop
it.

Related: https://gitlab.freedesktop.org/freedesktop/ci-templates/-/issues/81
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/430>

.gitlab-ci.yml

@@ -41,7 +41,6 @@ variables:
 .prereview-req:
   needs:
     - check-commit-log
-    - check-merge-request
 
 check-commit-log:
   extends:
@@ -63,26 +62,6 @@ check-commit-log:
     reports:
       junit: commit-message-junit-report.xml
 
-check-merge-request:
-  extends:
-    - .fdo.ci-fairy
-  stage: pre-review
-  script:
-    - if [[ x"$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" != "x" ]] ;
-      then
-        ci-fairy check-merge-request --require-allow-collaboration --junit-xml=check-merge-request-report.xml ;
-      else
-        echo "Not a merge request" ;
-      fi
-  rules:
-    - !reference [.pipeline-guard, rules]
-  artifacts:
-    expire_in: 1 week
-    paths:
-      - check-merge-request-report.xml
-    reports:
-      junit: check-merge-request-report.xml
-
 check-reuse:
   stage: pre-review
   image: