[interf] Don't record "ill-typed" interferences.

The coloring algorithm uses only the "well-typed" interferences (registers
with same class). This is because we don't assign the same stack slot to
registers of different register class.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13207 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
[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