CLN: remove internal usage of integer_array()
The `integer_array()` function stems from a time that `pd.array(..)` didn't exist yet. But since now `pd.array` can do this, IMO we shouldn't be using that outside of the integer module (eg I didn't add a `floating_array(..)`).

Only in `tests/arrays/integer/tst_construction.py` I still left the usage of `integer_array()` as is (but probably could also change it there). Could in principle remove the function altogether, since it is just a small wrapper around the private `arrays.integer.coerce_to_array`