[coloring] No need to test for "well-typed" interferences.
The interference graph no longer contains "ill-typed" interferences
between registers of different class, so we no longer need to test
in the coloring algorithm.
git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13208 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02