APIv4 DELETE channels/{channel_id} (#5723)

i18n/en.json

@@ -303,6 +303,10 @@
     "id": "api.channel.join_channel.permissions.app_error",
     "translation": "You do not have the appropriate permissions"
   },
+  {
+    "id": "api.channel.join_channel.already_deleted.app_error",
+    "translation": "Channel is already deleted"
+  },
   {
     "id": "api.channel.join_channel.post_and_forget",
     "translation": "%v has joined the channel."