drop deprecated validation setting

Author: TheFox0x7

modules/metrics/collector.go

@@ -11,15 +11,10 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/common/model"
 )
 
 const namespace = "gitea_"
 
-func init() {
-	model.NameValidationScheme = model.UTF8Validation
-}
-
 // Collector implements the prometheus.Collector interface and
 // exposes gitea metrics for prometheus
 type Collector struct {