core: remove generic job completion messages from unit vtables

These units' message format strings are identical to the generic
strings. Since we can always rely on the fallback, these are now
redundant.

src/core/target.c

@@ -227,7 +227,6 @@ const UnitVTable target_vtable = {
         .status_message_formats = {
                 .finished_start_job = {
                         [JOB_DONE]       = "Reached target %s.",
-                        [JOB_DEPENDENCY] = "Dependency failed for %s.",
                 },
                 .finished_stop_job = {
                         [JOB_DONE]       = "Stopped target %s.",