[Ada] Transient scope cleanup

[Ada] Transient scope cleanup

gcc/ada/

	* checks.adb, exp_attr.adb, exp_ch4.adb, exp_ch6.adb,
	exp_ch9.adb, exp_disp.adb, exp_util.adb, inline.adb,
	sem_res.adb: Change all calls to Make_Unchecked_Type_Conversion
	to call Unchecked_Convert_To instead. This involves removing
	New_Occurrence_Of on the first parameter, because
	Unchecked_Convert_To expects a type entity, rather than the name
	of one. Also, removed calls to Relocate_Node, because
	Unchecked_Convert_To takes care of that.
	* sinfo.ads: Change comment to be worded more firmly.