Drop rest client request latecy metric

In an effort to reduce the storage for nonessential memory-intensive
metrics, rest_client_request_latency_seconds was identified as the
metric that reports and stores the most time series
This metric has been deprecated since kube 1.14 and turned off in
kube 1.17

pkg/metrics/client_go_adapter.go

@@ -17,9 +17,6 @@ limitations under the License.
 package metrics
 
 import (
-	"net/url"
-	"time"
-
 	"github.com/prometheus/client_golang/prometheus"
 	reflectormetrics "k8s.io/client-go/tools/cache"
 	clientmetrics "k8s.io/client-go/tools/metrics"
@@ -32,7 +29,6 @@ import (
 // Metrics subsystem and all of the keys used by the rest client.
 const (
 	RestClientSubsystem = "rest_client"
-	LatencyKey          = "request_latency_seconds"
 	ResultKey           = "requests_total"
 )
 
@@ -51,13 +47,6 @@ const (
 
 var (
 	// client metrics
-	requestLatency = prometheus.NewHistogramVec(prometheus.HistogramOpts{
-		Subsystem: RestClientSubsystem,
-		Name:      LatencyKey,
-		Help:      "Request latency in seconds. Broken down by verb and URL.",
-		Buckets:   prometheus.ExponentialBuckets(0.001, 2, 10),
-	}, []string{"verb", "url"})
-
 	requestResult = prometheus.NewCounterVec(prometheus.CounterOpts{
 		Subsystem: RestClientSubsystem,
 		Name:      ResultKey,
@@ -126,13 +115,11 @@ func init() {
 // registerClientMetrics sets up the client latency metrics from client-go
 func registerClientMetrics() {
 	// register the metrics with our registry
-	Registry.MustRegister(requestLatency)
 	Registry.MustRegister(requestResult)
 
 	// register the metrics with client-go
 	clientmetrics.Register(clientmetrics.RegisterOpts{
-		RequestLatency: &latencyAdapter{metric: requestLatency},
-		RequestResult:  &resultAdapter{metric: requestResult},
+		RequestResult: &resultAdapter{metric: requestResult},
 	})
 }
 
@@ -158,14 +145,6 @@ func registerReflectorMetrics() {
 // copied (more-or-less directly) from k8s.io/kubernetes setup code
 // (which isn't anywhere in an easily-importable place).
 
-type latencyAdapter struct {
-	metric *prometheus.HistogramVec
-}
-
-func (l *latencyAdapter) Observe(verb string, u url.URL, latency time.Duration) {
-	l.metric.WithLabelValues(verb, u.String()).Observe(latency.Seconds())
-}
-
 type resultAdapter struct {
 	metric *prometheus.CounterVec
 }