ada: Deconstruct support for abstract states with Relaxed_Initialization

ada: Deconstruct support for abstract states with Relaxed_Initialization

GNATprove newer implemented support for abstract states with aspect
Relaxed_Initialization, so the frontend support is now deconstructed.

gcc/ada/

	* einfo-utils.adb (Is_Relaxed_Initialization_State): Remove.
	* einfo-utils.ads (Is_Relaxed_Initialization_State): Remove.
	* einfo.ads: Remove description of removed aspect.
	* fe.h (Is_Relaxed_Initialization_State): Remove.
	* sem_prag.adb (Analyze_Abstract_State): Remove support for
	Relaxed_Initialization.
	* sem_util.adb (Has_Relaxed_Initialization): Likewise.
	* sem_util.ads (Has_Relaxed_Initialization): Likewise.