[Ada] Avoid redundant checks for empty lists

[Ada] Avoid redundant checks for empty lists

gcc/ada/

	* exp_ch4.adb (Expand_N_Expression_With_Actions): Avoid
	redundant check.
	* exp_ch5.adb (Expand_N_If_Statement): Likewise.
	* exp_ch7.adb (Process_Declarations): Likewise.
	* sem_elab.adb (Freeze_Node_Location): Likewise.
	* exp_util.adb (Insert_Actions): Likewise.
	(Is_OK_PF_Pragma): Likewise.
	(Requires_Cleanup_Actions): Remove early exit; ordinary
	processing path will similarly do nothing.