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/swap.c

@@ -1505,7 +1505,6 @@ const UnitVTable swap_vtable = {
                 .finished_start_job = {
                         [JOB_DONE]       = "Activated swap %s.",
                         [JOB_FAILED]     = "Failed to activate swap %s.",
-                        [JOB_DEPENDENCY] = "Dependency failed for %s.",
                         [JOB_TIMEOUT]    = "Timed out activating swap %s.",
                 },
                 .finished_stop_job = {