ada: Tech debt: Remove exception handling from aspects

ada: Tech debt: Remove exception handling from aspects

Remove the Aspect_Exit exception and related code.
The big hammer of exceptions is not needed here,
and it gets in the way of future refactoring.
Some comments were slightly wrong; remove them instead of fixing
them.

gcc/ada/ChangeLog:

	* sem_ch13.adb (Analyze_One_Aspect): Remove the exception
	declaration, raises, and handler. Inline the code in
	Check_Expr_Is_OK_Static_Expression, which was called only once.