Add back in express extra dependencies and required dependencies

[marthacryan]

Fixes #5041 - @LiamConnors I haven't tested this through the CI artifacts yet but locally these changes are working for me!

Edit: tested the CI artifact and it's also working. Also, check out what it looks like in test.pypi.org! https://test.pypi.org/project/plotly/

[emilykl]

Are we OK with getting rid of standalone requires-install and requires-express files? I can't think of any reason why it should be an issue, but not sure why we had them in the first place.

@marthacryan Make sure to remove them from MANIFEST.in.

[marthacryan]

@emilykl Those files were used as arguments for the setup.py, but they had so few requirements in them that I felt like it made more sense to just put them inline. It shouldn't cause any issues for anyone.

Also, I'll remove them from the MANIFEST.in~

[emilykl]

LGTM! 🚀