Fix: unregister metrics

Author: zh_yu

qmq-metrics-prometheus/src/main/java/qunar/tc/qmq/metrics/prometheus/PrometheusQmqMetricRegistry.java

@@ -99,9 +99,9 @@ public QmqTimer newTimer(final String name, final String[] tags, final String[]
 
     @Override
     public void remove(final String name, final String[] tags, final String[] values) {
-        // TODO(keli.wang): only remove child collectors for now, may we should remove whole metric in the future
-        final SimpleCollector collector = cacheFor(new SimpleCollectorKey(name, tags));
-        collector.remove(values);
+        final Collector collector = CACHE.getIfPresent(new SimpleCollectorKey(name, tags));
+        if (collector == null) return;
+        CollectorRegistry.defaultRegistry.unregister(collector);
     }
 
     private static abstract class Key<M extends Collector> {
@@ -145,7 +145,7 @@ private static class SimpleCollectorKey extends Key<SimpleCollector> {
 
         @Override
         public SimpleCollector create() {
-            throw new UnsupportedOperationException("cannot create simple collector");
+            return null;
         }
     }