style: Remove -moz-user-disabled.

We treat it exactly the same as -moz-broken. The pseudo-class is not
exposed to content, so I don't think we have a reason to keep it around.

Differential Revision: https://phabricator.services.mozilla.com/D89904

components/style/gecko/wrapper.rs

@@ -2029,7 +2029,6 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::Invalid |
             NonTSPseudoClass::MozUIValid |
             NonTSPseudoClass::MozBroken |
-            NonTSPseudoClass::MozUserDisabled |
             NonTSPseudoClass::MozSuppressed |
             NonTSPseudoClass::MozLoading |
             NonTSPseudoClass::MozHandlerBlocked |