Bug 1492958 - Remove user-select: -moz-all. r=mats

It's an attempt of an alias to `all`, except it doesn't get handled in all
places.

Seems unused both in comm-central and mozilla-central, and all external usage I
could find is followed by -webkit-user-select: all.

Differential Revision: https://phabricator.services.mozilla.com/D11582

layout/generic/nsFrame.cpp

@@ -4162,9 +4162,7 @@ nsIFrame::IsSelectable(StyleUserSelect* aSelectStyle) const
   while (frame) {
     const nsStyleUIReset* userinterface = frame->StyleUIReset();
     switch (userinterface->mUserSelect) {
-      case StyleUserSelect::All:
-      case StyleUserSelect::MozAll:
-      {
+      case StyleUserSelect::All: {
         // override the previous values
         if (selectStyle != StyleUserSelect::MozText) {
           selectStyle = userinterface->mUserSelect;
@@ -4188,8 +4186,6 @@ nsIFrame::IsSelectable(StyleUserSelect* aSelectStyle) const
   if (selectStyle == StyleUserSelect::Auto ||
       selectStyle == StyleUserSelect::MozText) {
     selectStyle = StyleUserSelect::Text;
-  } else if (selectStyle == StyleUserSelect::MozAll) {
-    selectStyle = StyleUserSelect::All;
   }
 
   // If user tries to select all of a non-editable content,

layout/style/test/property_database.js

@@ -2625,7 +2625,7 @@ var gCSSProperties = {
     inherited: false,
     type: CSS_TYPE_LONGHAND,
     initial_values: [ "auto" ],
-    other_values: [ "none", "text", "all", "-moz-all", "-moz-none" ],
+    other_values: [ "none", "text", "all", "-moz-none" ],
     invalid_values: []
   },
   "background": {

servo/components/style/values/specified/ui.rs

@@ -163,11 +163,8 @@ pub enum UserSelect {
     Text,
     #[parse(aliases = "-moz-none")]
     None,
-    All,
     /// Force selection of all children, unless an ancestor has `none` set.
-    ///
-    /// See bug 48096.
-    MozAll,
+    All,
     /// Like `text`, except that it won't get overridden by ancestors having
     /// `all`.
     MozText,