BUGFIX: fix dependencies in setup.py (#2605)
### Description
Currently the requirements associated with an extra in the `setup.py` is
being dynamically generated using the `load_requirements()` method in
the same file. This is being passed in all the `.in` files which then
get read line by line to generate the requirements associated with an
extra. Unless the `.in` file itself has a version pin, this will never
respect the `.txt` files being generated by `pip-compile`. This fix
updates all the inputs to `load_requirements()` to use the `.txt` files
themselves.
