Remove SECP256K1 deprecated context flags

[MementoRC]

Proposal to remove the deprecated CONTEXT flags

Source SECP256K1 include/secp256k1.h:
https://github.com/bitcoin-core/secp256k1/blob/e4af41c61b0bb55fc9614cb39df8e455715b4dd4/include/secp256k1.h#L207

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8bfb756) 85.45% compared to head (f6f48e2) 85.86%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #135      +/-   ##
==========================================
+ Coverage   85.45%   85.86%   +0.40%     
==========================================
  Files          10       11       +1     
  Lines         557      573      +16     
  Branches       66       66              
==========================================
+ Hits          476      492      +16     
  Misses         45       45              
  Partials       36       36              

Files	Coverage Δ
coincurve/context.py	80.00% <100.00%> (ø)
coincurve/flags.py	100.00% <100.00%> (ø)
coincurve/keys.py	76.76% <100.00%> (ø)
tests/test_ecdsa.py	100.00% <100.00%> (ø)
tests/test_flags.py	100.00% <100.00%> (ø)
tests/test_keys.py	100.00% <100.00%> (ø)
tests/test_utils.py	100.00% <100.00%> (ø)

[ofek]

What was the issue?

[MementoRC]

@ofek The #define xxx (value | value) may not be interpreted by CFFI on windows. Looking at older version I see that you had already hardcoded the integer value in _windows_libsecp256k1.py
Well, I have not been able to confirm that it is the issue

Also, for the missing cffi, I had moved it to the pyproject.toml, instead of in the setup.py with setup_requires, maybe that is the issue that darosior is having? meaning, not using requirements.txt (I thought he was doing a pip install -r requirements.txt)

[carterbox]

IMHO, these changes seem too extensive. The conda package which uses an external dynamically linked libsecp256k1 instead of a revended statically linked libsecp256k1 is able to be imported on Windows. That means the problem with the PYPI package (the difference between the PYPI and conda package) should be related to building and linking libsecp256k1 only.

[MementoRC]

There are several changes that are related but not necessary. I think the key issue was in the _windows_libsecp256k1.py, which is used in the PyPI build process and not in the conda build. I actually wonder if it is needed, perhaps it was needed only for previous version of CFFI

How to check that this will solve the issue? - My way was to implement a windows-wheel build/test, but it requires a lot of try/error, I don't mind going through it, but if a simpler way is available, it would be great

[MementoRC]

This PR is a bit too messy. Resubmitting in a more orderly fashion