[Ada] Revert recent changes in the generation of deps in ali files

Following the discovery of regressions in GPRbuild, this reverts both
r263100 and r264608:

2019-01-08  Justin Squirek  <squirek@adacore.com>

	Revert:

	2018-07-31  Justin Squirek  <squirek@adacore.com>

	gcc/ada/

		* lib-writ.adb (Write_With_Lines): Modfiy the generation
		of dependencies within ali files so that source unit
		bodies are properly listed even if said bodies are
		missing.  Perform legacy behavior in GNATprove mode.
		* lib-writ.ads: Modify documentation to reflect current
		behavior.

	and:

	2018-09-26  Justin Squirek  <squirek@adacore.com>

	gcc/ada/

		* lib-writ.adb, lib-writ.ads (Write_With_Lines): Add
		documentation and an extra conditional check for RCI
		units so that generated ali files will list the spec
		only instead of a body when a body is not found.

From-SVN: r267680