Remove unused internal member, shows that Config.DefaultHistogramBoun…

…daries is unused (#2765)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

Co-authored-by: Chester Cheung <cheung.zhy.csu@gmail.com>

exporters/prometheus/prometheus.go

@@ -53,8 +53,6 @@ type Exporter struct {
 	// controllers (e.g., with different resources).
 	lock       sync.RWMutex
 	controller *controller.Controller
-
-	defaultHistogramBoundaries []float64
 }
 
 // ErrUnsupportedAggregator is returned for unrepresentable aggregator
@@ -104,11 +102,10 @@ func New(config Config, controller *controller.Controller) (*Exporter, error) {
 	}
 
 	e := &Exporter{
-		handler:                    promhttp.HandlerFor(config.Gatherer, promhttp.HandlerOpts{}),
-		registerer:                 config.Registerer,
-		gatherer:                   config.Gatherer,
-		controller:                 controller,
-		defaultHistogramBoundaries: config.DefaultHistogramBoundaries,
+		handler:    promhttp.HandlerFor(config.Gatherer, promhttp.HandlerOpts{}),
+		registerer: config.Registerer,
+		gatherer:   config.Gatherer,
+		controller: controller,
 	}
 
 	c := &collector{