Iteration with an artificial Continue flag in routine Validated_View was
confusing. Also, most of the routines that traverse type hierarchies are
written in recursive style.

Cleanup only; semantics is unaffected.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_util.ads (Validated_View): Fix style in comment.
	* sem_util.adb (Validated_View): Rewrite in recursive style.