Don't add promrus hook (#754)

We have overlapping functionality in cortex/pkg/util/log.go

Author: bboreham

cmd/distributor/main.go

@@ -9,7 +9,6 @@ import (
 	"github.com/opentracing-contrib/go-stdlib/nethttp"
 	"github.com/opentracing/opentracing-go"
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/common/log"
 	"google.golang.org/grpc"
 
 	"github.com/weaveworks/common/middleware"
@@ -18,7 +17,6 @@ import (
 	"github.com/weaveworks/cortex/pkg/distributor"
 	"github.com/weaveworks/cortex/pkg/ring"
 	"github.com/weaveworks/cortex/pkg/util"
-	"github.com/weaveworks/promrus"
 )
 
 func main() {
@@ -60,8 +58,6 @@ func main() {
 	trace := tracing.New(jaegerAgentHost, "distributor")
 	defer trace.Close()
 
-	log.AddHook(promrus.MustNewPrometheusHook())
-
 	r, err := ring.New(ringConfig)
 	if err != nil {
 		level.Error(util.Logger).Log("msg", "error initializing ring", "err", err)