remove more global refs (#7480)

einterfaces/metrics.go

@@ -38,13 +38,3 @@ type MetricsInterface interface {
 	AddMemCacheHitCounter(cacheName string, amount float64)
 	AddMemCacheMissCounter(cacheName string, amount float64)
 }
-
-var theMetricsInterface MetricsInterface
-
-func RegisterMetricsInterface(newInterface MetricsInterface) {
-	theMetricsInterface = newInterface
-}
-
-func GetMetricsInterface() MetricsInterface {
-	return theMetricsInterface
-}