[Ada] Consolidate handling of implicit dereferences

[Ada] Consolidate handling of implicit dereferences

2020-06-19  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* gcc-interface/trans.c (adjust_for_implicit_deref): Delete.
	(maybe_implicit_deref): Likewise.
	(Attribute_to_gnu): Replace calls to maybe_implicit_deref by calls
	to maybe_padded_object.
	(Call_to_gnu): Likewise.
	(gnat_to_gnu) <N_Indexed_Component>: Likewise.
	<N_Slice>: Likewise.
	<N_Selected_Component>: Likewise.
	<N_Free_Statement>: Remove call to adjust_for_implicit_deref and
	manually make sure that the designated type is complete.
	* gcc-interface/utils2.c (build_simple_component_ref): Add comment.