[CLEANUP] Remove superfluous commented test in SelectorTest (#1503)

Rejecting whitespace-only selectors was fixed in #1502.

Author: JakeQZ

tests/Unit/Property/SelectorTest.php

@@ -173,8 +173,6 @@ public static function provideInvalidSelectors(): array
             // 'dot only' => ['.'],
             'slash' => ['/'],
             'less-than sign' => ['<'],
-            // This is currently broken.
-            // 'whitespace only' => [" \t\n\r"],
         ];
     }