skins.vector.styles: Remove PNG fallback and merge skins.vector.icons module

* Remove the PNG fallbacks for chevronHorizontal-….svg and menu.svg.

  As of T248061, these are no longer needed.

* Added the one line of trivial CSS directly to skins.vector.styles
  instead of through its own module.

  This helps recovers the module cost of vue module deployed this
  week (from  Ib6c8f890fb3d6e7), which is currently empty and unused.

  With T253582, we'll be able to recover a lot more budget in
  this area.

Bug: T258766
Change-Id: I6bc4cf541eefd00e2e428f918664a26da331c1a9

bundlesize.config.json

@@ -5,11 +5,7 @@
 	},
 	{
 		"resourceModule": "skins.vector.styles",
-		"maxSize": "8.7 kB"
-	},
-	{
-		"resourceModule": "skins.vector.icons",
-		"maxSize": "0.6 kB"
+		"maxSize": "9.0 kB"
 	},
 	{
 		"resourceModule": "skins.vector.styles.responsive",

resources/skins.vector.styles/Sidebar.less

@@ -38,6 +38,13 @@
 		margin: 0 @margin-horizontal-sidebar-button-icon;
 		// Equals `#555`, closest to `#54595d` on background-color `#fff`.
 		opacity: 0.67;
+		/* @embed */
+		background-image: linear-gradient( transparent, transparent ), url( images/chevronHorizontal-ltr.svg );
+
+		#mw-sidebar-checkbox:not( :checked ) ~ .mw-header & {
+			/* @embed */
+			background-image: linear-gradient( transparent, transparent ), url( images/menu.svg );
+		}
 	}
 
 	&:hover {

skin.json

@@ -26,8 +26,7 @@
 					],
 					"styles": [
 						"skins.vector.styles",
-						"mediawiki.ui.icon",
-						"skins.vector.icons"
+						"mediawiki.ui.icon"
 					],
 					"messages": [
 						"vector-action-toggle-sidebar",
@@ -85,19 +84,6 @@
 			],
 			"styles": [ "resources/skins.vector.styles/skin.less" ]
 		},
-		"skins.vector.icons": {
-			"class": "ResourceLoaderImageModule",
-			"selector": "{name}",
-			"images": {
-				"#mw-sidebar-button:before": {
-					"file": {
-						"ltr": "resources/skins.vector.icons/chevronHorizontal-ltr.svg",
-						"rtl": "resources/skins.vector.icons/chevronHorizontal-rtl.svg"
-					}
-				},
-				"#mw-sidebar-checkbox:not( :checked ) ~ .mw-header #mw-sidebar-button:before": "resources/skins.vector.icons/menu.svg"
-			}
-		},
 		"skins.vector.styles.responsive": {
 			"targets": [
 				"desktop",