Reverted back to remove transitive closure

Ignoring proper C denpendencies.

Say foo.dats <- bar.dats, but foo.dats is not in the source list to be compiled. Then foo_dats.c <- bar_dats.c will not be generated.

This is done in the ATS_DEPGEN_C, by checking whether foo.dats is in the source list (of ATS_COMPILE). (reverted from commit ac97604753fda7692a9089f304686deecd565932)