build: deduplicate sources

Shorten the needed sources from

 calls_sources, calls_enum_sources, calls_resources,
 wl_proto_sources, wayland_sources,

to

  calls_sources

so adding new things such as generated dbus sources doesn't have to happen in four locations but just one.

There was heaps of duplication and each new test broke things again due to incomplete sources. Consolidate this. I would have postponed but this makes rebases simpler.