Remove unreferenced skin style

Follow up to I9c87f6a676186928787c130e61d3c312214e1853
which removed the reference but not the file

Bug: T208340
Change-Id: I416062a7ee48dd00a705abee2675f781491c3e00

skinStyles/mediawiki.special.preferences.styles/styles.less

@@ -1,59 +0,0 @@
-@import '../../minerva.less/minerva.variables';
-
-// FIXME: All this code can be removed when T117781/T171238 is resolved.
-#preftoc {
-	text-align: left;
-	// Horizontal scrolling
-	overflow-x: auto;
-	overflow-y: hidden;
-	white-space: nowrap;
-	padding: 0;
-
-	li {
-		display: inline-block;
-		color: @colorGray2;
-		border: 1px solid @colorFieldBorder;
-		border-radius: 0;
-
-		&:first-child {
-			border-top-left-radius: 2px;
-			border-bottom-left-radius: 2px;
-		}
-
-		&:last-child {
-			border-top-right-radius: 2px;
-			border-bottom-right-radius: 2px;
-		}
-
-		&:not( :first-child ) {
-			border-left: 0;
-		}
-
-		&.selected {
-			background-color: @colorProgressiveActive;
-			border-color: @colorProgressiveActive;
-			color: #fff;
-			box-shadow: none;
-		}
-
-		a {
-			padding: 0.5em 1em;
-			color: inherit;
-			display: block;
-		}
-	}
-}
-
-// redudant on mobile - tab labels provide context
-.mainLegend {
-	display: none;
-}
-
-.mw-htmlform-submit-buttons,
-.mw-input {
-	select,
-	input {
-		border: solid 1px @colorFieldBorder;
-		padding: 8px;
-	}
-}