fix(item-divider): removal of unneeded margin unset (#27042)

## Pull request checklist

Please check if your PR fulfills the following requirements:
- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been reviewed and added / updated if needed (for bug
fixes / features)
- Some docs updates need to be made in the `ionic-docs` repo, in a
separate PR. See the [contributing
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for details.
- [x] Build (`npm run build`) was run locally and any changes were
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- [x] Lint (`npm run lint`) has passed locally and any fixes were made
for failures


## Pull request type

Please check the type of change your PR introduces:
- [x] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, renaming)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Build related changes
- [ ] Documentation content changes
- [ ] Other (please describe): 


## What is the current behavior?

End slots are lacking margin of 2px when in RTL.

Issue URL: Part of #17012  


## What is the new behavior?

- Simplifying `property-horizontal` by removing any margin unset

End slots with buttons will have a margin-end of 2px regardless of
direction.

### Screenshots

![Screen Shot 2023-03-24 at 13 48
25](https://user-images.githubusercontent.com/13530427/227642440-acf0f2c2-37c7-43da-bad4-67ef1b31b3ac.png)
![Screen Shot 2023-03-24 at 13 48
17](https://user-images.githubusercontent.com/13530427/227642445-79cf2986-c0b5-45d1-ba38-1beda698c2d5.png)


## Does this introduce a breaking change?

- [ ] Yes
- [x] No



## Other information

- Continuation of ionic-team/ionic-framework#27024 in order to apply it
to Framework v7

---------

Co-authored-by: Liam DeBeasi <liamdebeasi@users.noreply.github.com>
Co-authored-by: ionitron <hi@ionicframework.com>

core/src/themes/ionic.mixins.scss

@@ -242,27 +242,11 @@
     #{$prop}-right: $end;
 
   } @else {
-    #{$prop}-left: $start;
-    #{$prop}-right: $end;
-
-    @at-root {
-      @supports ((margin-inline-start: 0) or (-webkit-margin-start: 0)) {
-        & {
-          @if $start != null {
-            #{$prop}-left: unset;
-          }
-          @if $end != null {
-            #{$prop}-right: unset;
-          }
-
     -webkit-#{$prop}-start: $start;
     #{$prop}-inline-start: $start;
     -webkit-#{$prop}-end: $end;
     #{$prop}-inline-end: $end;
   }
-      }
-    }
-  }
 }
 
 // Add property for all directions