[#1689] ci: Move commit checker out of Jenkinsfile

Commit checker is now configured globally for all Gerrit repositories:
  TrueCloudLab/jenkins#16

This allows us to execute commit-checker independently from the rest of
CI suite and re-check commit message format without rerunning other
tests.

Change-Id: Ib8f899b856482a5dc5d03861171585415ff6b452
Signed-off-by: Vitaliy Potyarkin <v.potyarkin@yadro.com>

.ci/Jenkinsfile

@@ -78,10 +78,4 @@ async {
             }
         }
     }
-
-    task('dco') {
-        container('git.frostfs.info/truecloudlab/commit-check:master') {
-            sh 'FROM=pull_request_target commit-check'
-        }
-    }
 }