[Ada] Remove unnecessary guards for non-empty lists

[Ada] Remove unnecessary guards for non-empty lists

gcc/ada/

	* errout.adb (Remove_Warning_Messages): Remove unnecessary guard.
	* exp_util.adb (Kill_Dead_Code): Likewise.
	* par_sco.adb (Traverse_Declarations_Or_Statements): Likewise.
	* sem_ch3.adb (Build_Derived_Record_Type): Likewise.
	* sem_ch4.adb (Traverse_Interfaces): Likewise.
	* sem_eval.adb (Traverse_Interfaces): Likewise.
	* sem_util.adb (Collect_Interfaces): Likewise.
	(Has_Non_Null_Statements, Side_Effect_Free_Statements):
	Likewise; turn into WHILE loops, for consistency.