feat: channel delete 기능추가

src/components/channel/existingChannel.js

@@ -46,7 +46,7 @@ const ExistingChannel=({isOpen, onClose, data})=>{
   const handleDeleteChannel = async () => {
     try {
   
-      const response = await fetch(`api/channels/${userData.userId}`, {
+      const response = await fetch(`api/channels/`, {
         method: 'DELETE',
         headers: {
           'Content-Type': 'application/json',