util/cmpx: delete now that we're using Go 1.22

Updates #11058

Change-Id: I09dea8e86f03ec148b715efca339eab8b1f0f644
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/dnscache/messagecache.go

@@ -4,6 +4,7 @@
 package dnscache
 
 import (
+	"cmp"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -13,7 +14,6 @@ import (
 
 	"github.com/golang/groupcache/lru"
 	"golang.org/x/net/dns/dnsmessage"
-	"tailscale.com/util/cmpx"
 )
 
 // MessageCache is a cache that works at the DNS message layer,
@@ -60,7 +60,7 @@ func (c *MessageCache) Flush() {
 // pruneLocked prunes down the cache size to the configured (or
 // default) max size.
 func (c *MessageCache) pruneLocked() {
-	max := cmpx.Or(c.cacheSizeSet, 500)
+	max := cmp.Or(c.cacheSizeSet, 500)
 	for c.cache.Len() > max {
 		c.cache.RemoveOldest()
 	}