p2p/dnsdisc: using clear builtin func (#29418)

Co-authored-by: Felix Lange <[email protected]>

Author: cuiweixie

p2p/dnsdisc/client_test.go

@@ -215,7 +215,7 @@ func TestIteratorNodeUpdates(t *testing.T) {
 	// Ensure RandomNode returns the new nodes after the tree is updated.
 	updateSomeNodes(keys, nodes)
 	tree2, _ := makeTestTree("n", nodes, nil)
-	resolver.clear()
+	clear(resolver)
 	resolver.add(tree2.ToTXT("n"))
 	t.Log("tree updated")
 
@@ -256,7 +256,7 @@ func TestIteratorRootRecheckOnFail(t *testing.T) {
 	// Ensure RandomNode returns the new nodes after the tree is updated.
 	updateSomeNodes(keys, nodes)
 	tree2, _ := makeTestTree("n", nodes, nil)
-	resolver.clear()
+	clear(resolver)
 	resolver.add(tree2.ToTXT("n"))
 	t.Log("tree updated")
 
@@ -447,12 +447,6 @@ func newMapResolver(maps ...map[string]string) mapResolver {
 	return mr
 }
 
-func (mr mapResolver) clear() {
-	for k := range mr {
-		delete(mr, k)
-	}
-}
-
 func (mr mapResolver) add(m map[string]string) {
 	maps.Copy(mr, m)
 }