data: Remove copy-pasted handle_token from docs

This handle_token entry is not part of the *backend* API, only the
frontend.

Closes: #938

data/org.freedesktop.impl.portal.FileChooser.xml

@@ -212,13 +212,6 @@
 
       Supported keys in the @options vardict include:
 
-      * ``handle_token`` (``s``)
-
-        A string that will be used as the last element of the
-        @handle. Must be a valid object path element. See the
-        :ref:`org.freedesktop.portal.Request` documentation for more
-        information about the @handle.
-
       * ``accept_label`` (``s``)
 
         Label for the accept button. Mnemonic underlines are allowed.