These only worked before because our lowering of the `AAPCS` calling
convention was incorrect in a way which happened to match the ABI of
these functions. The tests aren't actually very helpful -- there are
already tests for `divmoddi4` etc -- so rather than using inline asm on
the caller side to match the ABI, we just delete these two tests.

We were for some reason missing a direct test for `__udivmodsi4`, so one
has been added.