Fix #1093 by moving requirements into environment.yml

[zrisher]

To fix #1093:

• I removed the contradicting pandas and numpy lines in requirements.txt.
• I then found that numba == 0.26.0 also implicity declares numpy>=1.7. Numba was also in the environment.yml, but without a version constraint, so I moved this there.
• six and toolz were declared in both places, so I removed them

That made requirements.txt empty, so I removed it. Happy to keep it in if preferred!

[codecov-io]

Current coverage is 98.79% (diff: 100%)

Merging #1094 into master will not change coverage

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[talumbau]

Ah, I see you did remove the requirements.txt. Ok, very good. Let's try it this way and see what breaks. I think the only possible issue will be what happens when I try to upload a new release to PyPI (https://pypi.python.org/pypi/taxcalc). If this breaks, I will find a way to fix it that does not involve creating a requirements.txt, since that eventually leads to dependencies specified in two places, which is bad.

[zrisher]

I think the only possible issue will be what happens when I try to upload a new release to PyPI (https://pypi.python.org/pypi/taxcalc). If this breaks, I will find a way to fix it

I would really appreciate that. I have no idea how the environment is created when this is built as a package. I imagine it has something to do with this line in setup.py:

 'install_requires': ['numpy', 'pandas'],

The Travis environment doesn't use environment.yml either, but rather requirements entered directly via the command line:

 - conda create -n taxcalcdev python=$TRAVIS_PYTHON_VERSION pytest setuptools pandas=0.18 toolz six mock bokeh

It would be awesome if we could unify the environments for local users, package users, and testing at some point.

[zrisher]

Just pushed a quick fix - the numba == 0.26.0 requirement was in that file from my local windows dev branch and accidently slipped into this PR. I removed it, so actually no changes to the environment.yml now, just the removal of requirements.txt.

[MattHJensen]

@talumbau, could you merge this if it looks good to you?

[talumbau]

looks good. merging.