refactor(aria/tree): removes random test styles

Updates to remove unnecessary styles.

Author: essjay05

src/components-examples/aria/tree/tree-common.css

@@ -66,7 +66,3 @@
 li[aria-expanded='false'] + ul[role='group'] {
   display: none;
 }
-
-.example-tree.ng-rtl {
-  background-color: red;
-}