Remove `text-shadow` from progressive mediawiki.ui buttons

Bug: T192303
Change-Id: If4023b2e5aff2635aba61b3bd9e1a280ed1c3908

resources/forms.less

@@ -144,7 +144,6 @@ button {
 	padding: 0.25em 1em 0.1em 1em;
 	border: solid 1px @grey;
 	border-bottom-width: @border;
-	text-shadow: 0 -1px 0 @grey;
 	box-sizing: border-box;
 	border-radius: @radius;
 	background: @background;
@@ -159,6 +158,11 @@ button {
 		background-color: @grey-bright;
 	}
 }
+input[ type='submit' ],
+input[ type='button' ],
+button {
+	text-shadow: 0 -1px 0 @grey;
+}
 textarea {
 	width: 100%;
 	resize: vertical;