This PR remove simp priorities that are not needed. Some of these will
probably cause complaints from the `simpNF` linter downstream in
Batteries, which I will re-address separately.
Proves
`Nat.mod_mul : x % (a * b) = x % a + a * (x / a % b)` and
`Nat.mod_pow_succ : x % b ^ (k + 1) = x % b ^ k + b ^ k * ((x / b ^ k) %
b)`, helpful for bitblasting.
