Remove vestigial reference to CollectedClientData/clientExtensions (#835

)

Merging per decision on 14-Mar-18 call

index.bs

@@ -3745,9 +3745,8 @@ Note: Extensions should aim to define authenticator arguments that are as small
 ## <dfn>Client extension processing</dfn> ## {#sctn-client-extension-processing}
 
 Extensions MAY define additional processing requirements on the client platform during the creation of credentials or the
-generation of an assertion. The [=client extension input=] for the extension is used an input to this client processing.
-Supported [=client extensions=] are recorded as a dictionary in the [=client data=] with the key
-{{CollectedClientData/clientExtensions}}. For each such extension, the client adds an entry to this dictionary with the
+generation of an assertion. The [=client extension input=] for the extension is used as an input to this client processing.
+For each supported [=client extension=], the client adds an entry to the |clientExtensions|  [=map=] with the
 [=extension identifier=] as the key, and the extension's [=client extension input=] as the value.
 
 Likewise, the [=client extension outputs=] are represented as a dictionary in the result of {{PublicKeyCredential/getClientExtensionResults()}}