fix: remove unsued metric 'optimal304DiffingCounter' (#5810)

This metric was used while developing the optimal304 feature. The
feature flag has been removed and this data is not longer being
collected and this will remove the metric from Prometheus.

src/lib/metrics.ts

@@ -195,12 +195,6 @@ export default class MetricsMonitor {
             labelNames: ['sdk_name', 'sdk_version'],
         });
 
-        const optimal304DiffingCounter = new client.Counter({
-            name: 'optimal_304_diffing',
-            help: 'Count the Optimal 304 diffing with status',
-            labelNames: ['status'],
-        });
-
         const productionChanges30 = new client.Gauge({
             name: 'production_changes_30',
             help: 'Changes made to production environment last 30 days',
@@ -361,10 +355,6 @@ export default class MetricsMonitor {
             schedulerDuration.labels(jobId).observe(time);
         });
 
-        eventBus.on('optimal304Differ', ({ status }) => {
-            optimal304DiffingCounter.labels(status).inc();
-        });
-
         eventBus.on(events.DB_TIME, ({ store, action, time }) => {
             dbDuration.labels(store, action).observe(time);
         });