Remove worker label from puma terminations metric

lib/gitlab/cluster/puma_worker_killer_observer.rb

@@ -15,9 +15,7 @@ module Gitlab
       private
       def log_termination(worker)
-        labels = { worker: "worker_#{worker.index}" }
-
-        @counter.increment(labels)
+        @counter.increment
       end
     end
   end

spec/lib/gitlab/cluster/puma_worker_killer_observer_spec.rb

@@ -17,9 +17,7 @@ describe Gitlab::Cluster::PumaWorkerKillerObserver do
     it 'increments timeout counter' do
       worker = double(index: 0)
-      expect(counter)
-        .to receive(:increment)
-        .with({ worker: 'worker_0' })
+      expect(counter).to receive(:increment)
       subject.callback.call(worker)
     end