app/vmselect/promql: remove metric name after applying ceil, floor and round functions in order to be more consistent with Prometheus

This improves VictoriaMetrics score at https://promlabs.com/promql-compliance-test-results-victoriametrics/

app/vmselect/promql/transform.go

@@ -18,11 +18,8 @@ import (
 )
 
 var transformFuncsKeepMetricGroup = map[string]bool{
-	"ceil":      true,
 	"clamp_max": true,
 	"clamp_min": true,
-	"floor":     true,
-	"round":     true,
 }
 
 var transformFuncs = map[string]transformFunc{