fix(@clayui/css): Forms c-unset/clay-unset shouldn't output anything …

…for $form-control-select-palette

packages/clay-css/src/scss/components/_forms.scss

@@ -297,14 +297,16 @@ select.form-control[multiple] {
 // Form Control Select Variants
 
 @each $key, $value in $form-control-select-palette {
-	$selector: if(
-		starts-with($key, '.') or starts-with($key, '#'),
-		$key,
-		str-insert($key, '.', 1)
-	);
-
-	#{$selector} {
-		@include clay-select-variant($value);
+	@if not clay-is-map-unset($value) {
+		$selector: if(
+			starts-with($key, '.') or starts-with($key, '#'),
+			$key,
+			str-insert($key, '.', 1)
+		);
+
+		#{$selector} {
+			@include clay-select-variant($value);
+		}
 	}
 }