instancehealth: remove monitoring check (#920)

Removes usage of the endpoint deprecated in https://github.com/sourcegraph/sourcegraph/pull/46299, related to sourcegraph/customer#1525

internal/instancehealth/checks.go

@@ -2,7 +2,6 @@ package instancehealth
 
 import (
 	"fmt"
-	"strings"
 	"time"
 
 	"github.com/sourcegraph/sourcegraph/lib/errors"
@@ -31,11 +30,6 @@ func NewChecks(
 			defer b.Close()
 			return checkSiteConfiguration(b, instanceHealth)
 		},
-		func(out *output.Output) error {
-			b := out.Block(output.Styled(output.StyleBold, "Monitoring alerts"))
-			defer b.Close()
-			return checkMonitoringAlerts(b, since, instanceHealth)
-		},
 		func(out *output.Output) error {
 			b := out.Block(output.Styled(output.StyleBold, "External services"))
 			defer b.Close()
@@ -86,33 +80,6 @@ func checkSiteConfiguration(
 	return nil
 }
 
-// checkMonitoringAlerts indicates if there are any alerts issued by monitoring infra
-func checkMonitoringAlerts(
-	out output.Writer,
-	since time.Duration,
-	instanceHealth Indicators,
-) error {
-	var criticalAlerts int
-	for _, a := range instanceHealth.Site.MonitoringStatistics.Alerts {
-		if a.Average == 0 || !strings.Contains(strings.ToLower(a.Name), "critical") {
-			continue
-		}
-		// average is ratio of 12h windows that alert was active, so we set the threshold
-		// if it's possible this alert could have been active in this 'since' window.
-		if a.Average*0.5 >= since.Hours()/12 {
-			criticalAlerts += 1
-			out.WriteLine(output.Linef(output.EmojiWarning, output.StyleWarning,
-				"Found recently active alert: %q", a.Name))
-		}
-	}
-	if criticalAlerts == 0 {
-		out.WriteLine(output.Emoji(output.EmojiSuccess, "No critical monitoring alerts!"))
-	}
-	// never error, just issue printed warning, since critical alerts aren't all _that_
-	// reliable today, though they provide a potentially useful signal.
-	return nil
-}
-
 // checkExternalServices checks the health of external service syncing
 func checkExternalServices(
 	out output.Writer,