fix(mixin-utils): remove std.prune and use std.filter instead

The use of `std.prune(std.map())` is slow and uses a big stack, on big
rulesets this can cause a 'RUNTIME ERROR: max stack frames exceeded.'.

It is better to use `std.filter()` to remove an element from an array.

Author: Duologic

mixin-utils/utils.libsonnet

@@ -392,10 +392,8 @@ local g = import 'grafana-builder/grafana.libsonnet';
       for group in groups
     ],
 
-  removeRuleGroup(ruleName):: {
-    local removeRuleGroup(rule) = if rule.name == ruleName then null else rule,
-    local currentRuleGroups = super.groups,
-    groups: std.prune(std.map(removeRuleGroup, currentRuleGroups)),
+  removeRuleGroup(groupName):: {
+    groups: std.filter(function(group) group.name != groupName, super.groups),
   },
 
   removeAlertRuleGroup(ruleName):: {
@@ -411,20 +409,17 @@ local g = import 'grafana-builder/grafana.libsonnet';
       if 'alert' in rule && std.objectHas(overrides, rule.alert)
       then rule + overrides[rule.alert]
       else rule,
-    local overrideInGroup(group) = group { rules: std.map(overrideRule, super.rules) },
+    local overrideInGroup(group) = group + { rules: std.map(overrideRule, super.rules) },
     prometheusAlerts+:: {
       groups: std.map(overrideInGroup, super.groups),
     },
   },
 
   removeAlerts(alerts):: {
-    local removeRule(rule) =
-      if 'alert' in rule && std.objectHas(alerts, rule.alert)
-      then {}
-      else rule,
-    local removeInGroup(group) = group { rules: std.map(removeRule, super.rules) },
+    local removeRule(rule) = !std.member(alerts, std.get(rule, 'alert', '')),
+    local removeInGroup(group) = group + { rules: std.filter(removeRule, super.rules) },
     prometheusAlerts+:: {
-      groups: std.prune(std.map(removeInGroup, super.groups)),
+      groups: std.map(removeInGroup, super.groups),
     },
   },
 }