Remove StructuedClone call

It was wrong for MediaSource and MediaStream objects, which cannot be
serialized and deserialized, and it’s no longer necessary for Blob
objects as their state cannot be modified. (And it’s also out-of-date
as HTML now has serialization and deserialization operations.)

Fixes #277.

url.bs

@@ -1377,9 +1377,8 @@ different document encoding. Using the <a>UTF-8</a> encoding everywhere solves t
  <a for=url>path</a>[0] is not in the <a>blob URL store</a>, then return <var>url</var>.
  [[!FILEAPI]]
 
- <li><p>Set <var>url</var>'s <a for=url>object</a> to a <a abstract-op>StructuredClone</a> of the
- entry in the <a>blob URL store</a> corresponding to <var>url</var>'s <a for=url>path</a>[0].
- [[!HTML]]
+ <li><p>Set <var>url</var>'s <a for=url>object</a> to the entry in the <a>blob URL store</a>
+ corresponding to <var>url</var>'s <a for=url>path</a>[0].
 
  <li><p>Return <var>url</var>.
 </ol>
@@ -3267,9 +3266,9 @@ neighboring rights to this work.
 urlPrefix: https://w3c.github.io/FileAPI/; type: dfn
     text: blob url store; url: #BlobURLStore
 urlPrefix: https://w3c.github.io/media-source/#idl-def-; type: interface
-    text: MediaSource; url: MediaSource
-urlPrefix: https://www.w3.org/TR/mediacapture-streams/#idl-def-; type: interface
-    text: MediaStream; url: MediaStream
+    text: MediaSource
+urlPrefix: https://w3c.github.io/mediacapture-main/#idl-def-; type: interface
+    text: MediaStream
 url: http://www.unicode.org/reports/tr46/#ToASCII; type: dfn; text: toascii; spec: IDNA
 url: http://www.unicode.org/reports/tr46/#ToUnicode; type: dfn; text: tounicode; spec: IDNA
 </pre>