scss: remove duplicated .pk-button and .pk-big-button selectors (#67858)

static/includes/_library.scss

@@ -6,11 +6,14 @@
 
 @import 'table';
 
-a.pk-button, a.pk-big-button {
-	@extend %button;
-	display: inline-block;
-	margin: 0;
-	height: auto;
+a {
+	&.pk-button, &.pk-big-button {
+		@extend %button;
+		display: inline-block;
+		margin: 0;
+		height: auto;
+	}
+
 	&.pk-button {
 		padding: 0.5rem 1rem;
 	}
@@ -19,14 +22,16 @@ a.pk-button, a.pk-big-button {
 	}
 }
 
-div.link-cell.pk-button,
-div.link-cell.pk-big-button {
-	ul > li > a {
-		@extend %button;
-		display: block;
-		margin: 0;
-		height: auto;
+div.link-cell {
+	&.pk-button, &.pk-big-button {
+		ul > li > a {
+			@extend %button;
+			display: block;
+			margin: 0;
+			height: auto;
+		}
 	}
+
 	&.pk-button ul > li > a {
 		padding: 0.5rem 1rem;
 	}