[Ada] Fix references to old variables that have been refactored

[Ada] Fix references to old variables that have been refactored

Local_Entity_Suppress and Global_Entity_Suppress variables referencing
tables were refactored to Local_Suppress_Stack_Top and
Global_Suppress_Stack_Top stacks back in 2007.  Fix remaining references
to these variables.

gcc/ada/

	* einfo.ads: Fix reference to Global_Entity_Suppress and
	Local_Entity_Suppress variable in the comments.
	* sem.ads: Likewise.
	* sem_prag.adb: Likewise.