deploy_gitlab_ci: revert trigger pipeline on integration branch

Explicitly triggering a pipeline in the target repository does not work
easily from this place because we would have to distinguish between the
manifest (which uses branch pipelines) and the sub-projects (which use
merge request pipelines). This separation should not be hard-coded here,
so we move the decision whether or not to run a pipeline to the
.gitlab-ci.yml file of the target. Reverting these two commits:

63279799
    deploy_gitlab_ci: trigger pipeline only if it has not run before

dfc6204a
    deploy_gitlab_ci: trigger pipeline on integration branch

deploy_gitlab_ci.py

@@ -3,7 +3,7 @@ import common
 
 import argparse
 import sys
-from gitlab import Gitlab, GitlabCreateError
+from gitlab import Gitlab
 from accept_merge_request import accept_merge_request
 from create_merge_request import create_merge_request
 from get_merge_requests import get_merge_requests
@@ -64,7 +64,7 @@ def main():
     project = common.get_project(gitlab, args.project)
 
     # Update submodule
-    integration_branch, integration_commit, submodule_project = update_submodule(
+    integration_branch, _, submodule_project = update_submodule(
         project, args.submodule, args.revision, args.branch
     )
 
@@ -91,14 +91,6 @@ def main():
     else:
         print("Existing integration merge request:\n%s" % mr.web_url)
 
-    # Explicitly trigger a pipeline on the integration branch if it has not run for the
-    # head commit yet (automatic pipelines are disabled for integration branches)
-    if not project.pipelines.list(sha=integration_commit):
-        try:
-            project.pipelines.create({"ref": integration_branch})
-        except GitlabCreateError as e:
-            sys.exit("ERROR: could not create merge request pipeline: %s" % e)
-
     if not args.merge:
         print(
             "Skipping automatic merge in MR context. If you like to extend the "