ada: Fix spurious warning emission

ada: Fix spurious warning emission

This patch fixes a bug where GNAT would emit incorrect warnings
about obsolescent syntax for array aggregates with generics and
particular arrangements of Ada version pragmas.

This patch also removes a syntactic field that was introduced to
support the emission of this warning, but is no longer required.

gcc/ada/

	* exp_imgv.adb (Append_Table_To): Remove reference to removed
	field.
	* gen_il-fields.ads: Remove Is_Enum_Array_Aggregate field.
	* gen_il-gen-gen_nodes.adb: Likewise.
	* sem_aggr.adb: Tweak warning emission condition.
	* sinfo.ads: Remove documentation for Is_Enum_Array_Aggregate.