python-brotli: Separate from brotli PKGBUILD and devendor brotli

The python binding could be built separately from the native library[1], which simplifies the PKGBUILD. The binding will also link to the dynamic library, instead of shipping a copy of brotli on its own.

[1]: https://github.com/google/brotli/blob/61af0e5b94e19d321561c6c21c9d9e0b997d7fb5/setup.py#L183-L322