Remove unnecessary pprof import (#14988)

The pattern of `import _ "net/http/pprof"` adds handlers to the default
http handler, but Prometheus does not use that. There are explicit
handlers in `web/web.go`.

So, we can remove this line with no impact to behaviour.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

cmd/prometheus/main.go

@@ -22,7 +22,6 @@ import (
 	"math/bits"
 	"net"
 	"net/http"
-	_ "net/http/pprof" // Comment this line to disable pprof endpoint.
 	"net/url"
 	"os"
 	"os/signal"