[Ada] Iterate with procedural versions of Next_... routines where possible

[Ada] Iterate with procedural versions of Next_... routines where possible

2020-06-03  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* checks.adb, einfo.adb, exp_aggr.adb, exp_ch4.adb, exp_ch6.adb,
	exp_unst.adb, exp_util.adb, freeze.adb, inline.adb, repinfo.adb,
	sem_aggr.adb, sem_attr.adb, sem_aux.adb, sem_ch13.adb,
	sem_ch3.adb, sem_ch4.adb, sem_ch8.adb, sem_elab.adb,
	sem_eval.adb, sem_prag.adb, sem_res.adb, sem_smem.adb,
	sem_util.adb, treepr.adb: Replace uses of Next_ functions with
	corresponding procedures.