Removed unused captions code.

skald-protocol.md

@@ -306,7 +306,7 @@ A chat message may be sent using a `chat` message.
 ```javascript
 {
     type: 'chat',
-    kind: null or 'me' or 'caption',
+    kind: null or 'me',
     source: source-id,
     username: username,
     dest: dest-id,
@@ -320,9 +320,7 @@ A chat message may be sent using a `chat` message.
 The field `kind` can have one of the following values:
 
   - `null` or the empty string, a normal chat message;
-  - `'me'`, an IRC-style first-person message;
-  - `'caption'`, a caption or subtitle (this requires the sender to have
-    the `caption` permission).
+  - `'me'`, an IRC-style first-person message.
 
 If `dest` is empty, the message is a broadcast message, destined to all of
 the clients in the hall.  If `source` is empty, then the message was