ada: Remove redundant conditions from freezing code

ada: Remove redundant conditions from freezing code

Code cleanup; behavior is unaffected.

gcc/ada/

	* freeze.adb (Check_Current_Instance): This routine is only called
	with parameter E being a type entity, so there is no need to check
	for types just before the equality with E.
	* sem_ch13.adb (Analyze_Aspect_Specifications): Regroup condition
	to avoid unnecessary evaluation.
	(Check_Aspect_At_End_Of_Declarations): If In_Instance is true,
	then the routine exits early.