Remove setuptools from install_requires

[hexponent]

I believe setuptools is redundant here.

Two reasons for that:

1. There are no mentions of setuptools (or other things distributed with it) in the code
2. If I build a wheel manually and than install it in a separate environment with no setuptools - not only it is installed successfully, but also importing fitbit and running some code (e.g. Fitbit.time_series) succeeds

[hexponent]

@brad please review. Is the project still maintained?