[x86] Remove a couple of fairly pointless tests. These were merely
testing that we generated divps and divss but not in a very systematic
way. There are other tests for widening binary operations already that
make these unnecessary.

The second one seems mostly about testing Atom as well as normal X86,
but despite the comment claiming it is testing a different instruction
sequence, it then tests for exactly the same div instruction sequence!
(The sequence of instructions is actually quite different on Atom, but
not the sequence of div instructions....)

And then it has an "execution" test that simply isn't run? Very strange.
Anyways, none of this is really needed so clean this up.
[x86] Add two more triples to stabilize the precise assembly syntax
across platforms.