RTL: Use much simpler approach to flip toolbar icons & preserve padding

We don't have to deal with background images attached to various parts of the
button like we did on macOS before, so we can just flip the icon and be done
with it.

scss/components/_toolbar.scss

@@ -6,35 +6,10 @@
 	min-width: 1px;
 }
 
-/* A decent hack: reverse the effective order of the dropmarker and icon in RTL
-   mode so that the above CSS, which places the menubutton-start.png background
-   on the toolbarbutton-icon, will make sense. (Otherwise the dropmarker appears
-   outside the button.) Then just flip the entire thing horizontally! We want to
-   do that anyway so that the Locate button will point to the left and Sync will
-   rotate counter-clockwise.
-
-   The other way to do this would be to set direction: ltr on buttons in the
-   RTL toolbar, but that breaks popup positioning. */
 :root:-moz-locale-dir(rtl) {
-	.zotero-tb-button > .toolbarbutton-menu-dropmarker {
-		-moz-box-ordinal-group: 0;
-	}
-
 	.zotero-tb-button > .toolbarbutton-icon {
-		-moz-box-ordinal-group: 1;
-	}
-
-	.zotero-tb-button,
-	.zotero-tb-button:first-child,
-	.zotero-tb-button:last-child {
 		transform: scaleX(-1);
 	}
-
-	@media not (-moz-platform: macos) {
-		.zotero-tb-button > .toolbarbutton-icon {
-			transform: scaleX(-1);
-		}
-	}
 }
 
 .zotero-toolbar {