Purge a number of Mozilla-specific WebIDL

Did a bunch of grepping for `moz*` and searched for "moz" in rustdoc,
deleting anything that looked mozilla-specific. Now there's nothing left
with the "moz" prefix in rustdoc!

crates/web-sys/webidls/enabled/CSSMozDocumentRule.webidl

@@ -3,8 +3,3 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/.
  */
-
-// This is a non-standard interface for @-moz-document rules
-interface CSSMozDocumentRule : CSSConditionRule {
-  // XXX Add access to the URL list.
-};