Remove generated C files from the repository

[kalekundert]

Currently, the repository contains 4 Cython-generated C source files. I think there are a few good reasons to remove these files:

• This thread gives a variety of opinions on whether generated files should be committed or not. The consensus is that there are some niche reasons to do this (e.g. the hand-written code is tightly coupled to the generated code, or the code generator is unreliable), but generally you shouldn't. I don't think any of the niche reasons apply here.
• Generated files can get out-of-date, and interfere with installation in confusing ways (as described in #26).
• Any commit made with a different version of Cython will have really big diffs. This obfuscates what actually changes in each commit, and it can easily lead to merge conflicts as well.

I can think of one possible reason to not remove these files, which is that they make the software more reproducible by ensuring that everyone gets the same generated source. But I don't think this is a very compelling reason:

• Without frequent updates (e.g. 2-3x per year), the generated source files get out-of-date and lead to the installation issues mentioned above. Frankly, this repository is just not updated frequently enough for this to work.
• Distributing the generated source files doesn't require checking them into the repository. It just requires including those files in the archive uploaded to PyPI.

I expect that merging either this PR or #30 will cause merge conflicts for the other. If/when this happens, I'll fix the conflicts.

[tscohen]

I agree, it makes more sense to remove these. Not sure why I chose to include them.... 7 years ago :)

Thanks for your contribution!