[#493] Refactor serving of prometheus and pprof services

Rename `util/profiler` package to `httputil` and refactor it:

  * simplify utility HTTP server;

  * make more generic server's parameters in order to remove `viper.Viper`
    dependency;

  * use single constructor for creating the pprof and prometheus servers;

  * replace `enabled` config value with empty-check of the network address.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

cmd/neofs-node/main.go

@@ -60,12 +60,10 @@ func initApp(c *cfg) {
 }
 
 func bootUp(c *cfg) {
-	serveProfiler(c)
 	serveGRPC(c)
 	bootstrapNode(c)
 	startWorkers(c)
 	startBlockTimers(c)
-	serveMetrics(c)
 }
 
 func wait(c *cfg) {