Auto merge of #16892 - pamadini:master, r=Manishearth

Allow -moz-stack-sizing to work in a single direction only.

<!-- Please describe your changes on the following line: -->
https://bugzilla.mozilla.org/show_bug.cgi?id=1364115
https://reviewboard.mozilla.org/r/138434/

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because these properties are not implemented

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16892)
<!-- Reviewable:end -->

components/style/properties/gecko.mako.rs

@@ -4339,16 +4339,7 @@ clip-path
 </%self:impl_trait>
 
 <%self:impl_trait style_struct_name="XUL"
-                  skip_longhands="-moz-stack-sizing -moz-box-ordinal-group">
-
-    #[allow(non_snake_case)]
-    pub fn set__moz_stack_sizing(&mut self, v: longhands::_moz_stack_sizing::computed_value::T) {
-        use properties::longhands::_moz_stack_sizing::computed_value::T;
-        self.gecko.mStretchStack = v == T::stretch_to_fit;
-    }
-
-    ${impl_simple_copy('_moz_stack_sizing', 'mStretchStack')}
-
+                  skip_longhands="-moz-box-ordinal-group">
     #[allow(non_snake_case)]
     pub fn set__moz_box_ordinal_group(&mut self, v: i32) {
         self.gecko.mBoxOrdinal = v as u32;