Disable audit event logging for pipeline destruction

AuditEventService isn't equipped to handle logging of the destruction of
entities such as CI pipelines. It's a project-level event that operates
on a pipeline. The current log doesn't even indicate that the pipeline
is being destroyed.

This is a CE backport of
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9105.  We're
removing the auditing call because it breaks the EE implementation.

app/services/ci/destroy_pipeline_service.rb

@@ -5,8 +5,6 @@ module Ci
     def execute(pipeline)
       raise Gitlab::Access::AccessDeniedError unless can?(current_user, :destroy_pipeline, pipeline)
 
-      AuditEventService.new(current_user, pipeline).security_event
-
       pipeline.destroy!
     end
   end

spec/requests/api/pipelines_spec.rb

@@ -456,8 +456,8 @@ describe API::Pipelines do
         expect(json_response['message']).to eq '404 Not found'
       end
 
-      it 'logs an audit event' do
-        expect { delete api("/projects/#{project.id}/pipelines/#{pipeline.id}", owner) }.to change { SecurityEvent.count }.by(1)
+      it 'does not log an audit event' do
+        expect { delete api("/projects/#{project.id}/pipelines/#{pipeline.id}", owner) }.not_to change { SecurityEvent.count }
       end
 
       context 'when the pipeline has jobs' do

spec/services/ci/destroy_pipeline_service_spec.rb

@@ -17,8 +17,8 @@ describe ::Ci::DestroyPipelineService do
       expect { pipeline.reload }.to raise_error(ActiveRecord::RecordNotFound)
     end
 
-    it 'logs an audit event' do
-      expect { subject }.to change { SecurityEvent.count }.by(1)
+    it 'does not log an audit event' do
+      expect { subject }.not_to change { SecurityEvent.count }
     end
 
     context 'when the pipeline has jobs' do