style: Nix -moz-user-input: disabled.

It does nothing, and there's only one use of it anyway.

See the intent to unship for research on out of the tree usage:

  https://groups.google.com/d/msg/mozilla.dev.platform/E6tfP__wkwg/YVW6nPX9CQAJ

Bug: 1405087
Reviewed-by: bz
MozReview-Commit-ID: 5XnsewYdvgQ

components/style/properties/longhand/pointing.mako.rs

@@ -21,7 +21,7 @@ ${helpers.single_keyword("pointer-events", "auto none", animation_value_type="di
                          flags="APPLIES_TO_PLACEHOLDER",
                          spec="https://www.w3.org/TR/SVG11/interact.html#PointerEventsProperty")}
 
-${helpers.single_keyword("-moz-user-input", "auto none enabled disabled",
+${helpers.single_keyword("-moz-user-input", "auto none enabled",
                          products="gecko", gecko_ffi_name="mUserInput",
                          gecko_enum_prefix="StyleUserInput",
                          animation_value_type="discrete",