remove workflow rules

I don't think these are actually necessary? At least in my own testing,
I haven't seen duplicate pipelines for a single commit when converting
from just a branch to a merge request.

.gitlab-ci.yml

@@ -173,13 +173,3 @@ test:audit:
     when: always
     reports:
       sast: gl-sast-report.json
-
-# Avoid duplicate pipelines
-# See: https://docs.gitlab.com/ee/ci/yaml/workflow.html#switch-between-branch-pipelines-and-merge-request-pipelines
-workflow:
-  rules:
-    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
-    - if: "$CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS"
-      when: never
-    - if: "$CI_COMMIT_BRANCH"
-    - if: "$CI_COMMIT_TAG"