Fix incomplete commit 9d388e

It left the Prometheus instrumentation in server/http.go, while
it is already provided by the ai3/go-common package.

server/http.go

@@ -18,8 +18,6 @@ import (
 	"github.com/gorilla/csrf"
 	"github.com/gorilla/mux"
 	"github.com/gorilla/sessions"
-	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/promhttp"
 
 	"git.autistici.org/id/auth"
 	authclient "git.autistici.org/id/auth/client"
@@ -64,8 +62,6 @@ func newAuthSession(ttl time.Duration, username string, userinfo *auth.UserInfo)
 
 func init() {
 	gob.Register(&authSession{})
-
-	prometheus.MustRegister(totalRequests, inFlightRequests)
 }
 
 // Returns the URL of the login handler on the target service.
@@ -278,13 +274,11 @@ func (h *Server) Handler() http.Handler {
 		AssetInfo: AssetInfo,
 		Prefix:    "static",
 	})))
-	m.Handle("/metrics", promhttp.Handler())
 
 	m.Handle("/exchange", withDynamicHeaders(http.HandlerFunc(h.handleExchange)))
 	m.Handle("/", withDynamicHeaders(h.withAuth(h.handleHomepage)))
 
-	return promhttp.InstrumentHandlerInFlight(inFlightRequests,
-		promhttp.InstrumentHandlerCounter(totalRequests, m))
+	return m
 }
 
 // A relatively strict CSP.
@@ -303,23 +297,6 @@ func withDynamicHeaders(h http.Handler) http.Handler {
 	})
 }
 
-// Instrumentation.
-var (
-	totalRequests = prometheus.NewCounterVec(
-		prometheus.CounterOpts{
-			Name: "total_requests",
-			Help: "Total number of requests.",
-		},
-		[]string{"code"},
-	)
-	inFlightRequests = prometheus.NewGauge(
-		prometheus.GaugeOpts{
-			Name: "inflight_requests",
-			Help: "Number of in-flight requests.",
-		},
-	)
-)
-
 // Parse the templates that are embedded with the binary (in bindata.go).
 func parseEmbeddedTemplates() *template.Template {
 	root := template.New("").Funcs(template.FuncMap{