Address #2185: Fix duplicated IDs for decode callbacks (#2253)

* Address #2185: Duplicate IDs for Decode callbacks

The decode callbacks were multiply defining their arguments.  Instead,
just have the descriptions of the arguments just link back to the IDL
that defines the args.

* Update expected errors

Author: rtoy

expected-errs.txt

@@ -1,7 +1,3 @@
-WARNING: Multiple elements have the same ID 'dom-decodeerrorcallback-error'.
-Deduping, but this ID may not be stable across revisions.
-WARNING: Multiple elements have the same ID 'dom-decodesuccesscallback-decodeddata'.
-Deduping, but this ID may not be stable across revisions.
 LINE: Can't find the 'contextOptions' argument of method 'OfflineAudioContext/constructor(numberOfChannels, length, sampleRate)' in the argumentdef block.
 LINE: Can't find the 'destinationNode' argument of method 'AudioNode/connect(destinationParam, output)' in the argumentdef block.
 LINE: Can't find the 'input' argument of method 'AudioNode/connect(destinationParam, output)' in the argumentdef block.

index.bs

@@ -1211,15 +1211,15 @@ Methods</h4>
 Callback {{DecodeSuccessCallback()}} Parameters</h4>
 
 <dl dfn-type=argument dfn-for="DecodeSuccessCallback()">
-	: <dfn>decodedData</dfn>, of type {{AudioBuffer}}
+	: {{DecodeSuccessCallback/decodedData!!argument}}</dfn>, of type {{AudioBuffer}}
 	:: The AudioBuffer containing the decoded audio data.
 </dl>
 
 <h4 id="callback-decodeerrorcallback-parameters" callback lt="DecodeErrorCallback()">
 Callback {{DecodeErrorCallback()}} Parameters</h4>
 
 <dl dfn-type=argument dfn-for="DecodeErrorCallback()">
-	: <dfn>error</dfn>, of type {{DOMException}}
+	: {{DecodeErrorCallback/error!!argument}}, of type {{DOMException}}
 	:: The error that occurred while decoding.
 </dl>