remove/deprecate crawler disable environment (#11214)

with changes present to automatically throttle crawler
at runtime, there is no need to have an environment
value to disable crawling. crawling is a fundamental
piece for healing, lifecycle and many other features
there is no good reason anyone would need to disable
this on a production system.

* Apply suggestions from code review

cmd/metrics.go

@@ -22,9 +22,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/minio/minio/cmd/config"
 	"github.com/minio/minio/cmd/logger"
-	"github.com/minio/minio/pkg/env"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
@@ -402,11 +400,6 @@ func bucketUsageMetricsPrometheus(ch chan<- prometheus.Metric) {
 		return
 	}
 
-	// Crawler disabled, nothing to do.
-	if env.Get(envDataUsageCrawlConf, config.EnableOn) != config.EnableOn {
-		return
-	}
-
 	dataUsageInfo, err := loadDataUsageFromBackend(GlobalContext, objLayer)
 	if err != nil {
 		return