This PR removes the deprecated aliases `Int.div := Int.tdiv` and
`Int.mod := Int.tmod`. Later we will rename `Int.ediv` to `Int.div` and
`Int.emod` to `Int.mod`.
I'd previously added an instance from `ForIn'` to `ForIn`, but this then
caused some non-defeq duplication. It seems fine to just remove the
concrete `ForIn` instances in cases where the `ForIn'` instance exists
too. We can even remove a number of type-specific lemmas in favour of
the general ones.
This feature produced counterintuitive behavior and confused users.
See discussion at #770.
As pointed out by @tydeu, it is not too much work to write `Id.run <|`
before the `do` when we want to use the `do` notation in pure code.
closes#770
