remove the STREAMLINK_USE_PYCRYPTO env var switch from setup.py
sort dependencies list
update dependencies section in install docs
- sort dependencies table
- rephrase notes column

pycrypto has had its last update in 2013
https://pypi.org/project/pycrypto/#history

As I've shown in #4170, there are no streamlink packages (anymore) which depend on pycrypto. If I missed one, then they will have to upgrade.

I included the updates for the docs in this commit because I don't want to post two PRs. I also removed the versions of non-build-dependencies from the docs because they were never up2date and it doesn't make sense having two lists for this. The only dependency list that matters is the one in setup.py (or setup.cfg if we move to a declarative list). Please take a look at the rendered docs preview to see if everything's okay.