Remove (de)serialization of no longer existent RTCEncodedVideoFrame.timestamp

follow up to #204
fix CI error noted in #140 (comment)

Author: dontcallmedom

index.bs

@@ -449,14 +449,12 @@ Their [=serialization steps=], given |value|, |serialized|, and |forStorage|, ar
 
 1. If |forStorage| is true, then throw a {{DataCloneError}}.
 1. Set |serialized|.`[[type]]` to the value of |value|.{{RTCEncodedVideoFrame/type}}
-1. Set |serialized|.`[[timestamp]]` to the value of |value|.{{RTCEncodedVideoFrame/timestamp}}
 1. Set |serialized|.`[[metadata]]` to an internal representation of |value|'s metadata.
 1. Set |serialized|.`[[data]]` to |value|.`[[data]]`
 
 Their [=deserialization steps=], given |serialized|, |value| and |realm|, are:
 
 1. Set |value|.{{RTCEncodedVideoFrame/type}} to |serialized|.`[[type]]`
-1. Set |value|.{{RTCEncodedVideoFrame/timestamp}} to |serialized|.`[[timestamp]]`
 1. Set |value|'s metadata to the platform object representation of |serialized|.`[[metadata]]`
 1. Set |value|.`[[data]]` to |serialized|.`[[data]]`.