Remove MANIFEST.in use auto-generated one for sdists and package_data for wheels

[vyasr]

Description

Using MANIFEST.in currently runs into a pretty nasty scikit-build bug (scikit-build/scikit-build#886) that results in any file included by the manifest being copied from the install tree back into the source tree whenever an in place build occurs after an install, overwriting any local changes. We need an alternative approach to ensure that all necessary files are included in built packages. There are two types:

• sdists: scikit-build automatically generates a manifest during sdist generation if we don't provide one, and that manifest is reliably complete. It contains all files needed for a source build up to the cudf C++ code (which has always been true and is something we can come back to improving later if desired).
• wheels: The autogenerated manifest is not used during wheel generation because the manifest generation hook is not invoked during wheel builds, so to include data in the wheels we must provide the package_data argument to setup. In this case we do not need to include CMake or pyx files because the result does not need to be possible to build from, it just needs pxd files for other packages to cimport if desired.

I also reverted #12945, which was a stopgap solution to avoid this underlying problem. That change would have caused import issues inside the python/cudf directory when installing (the lack of an inplace build would have made the source tree unimportable) so this fix removes that minor limitation introduced in that PR.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[bdice]

Please verify that this doesn't break #12945 -- then feel free to merge.

[vyasr]

/merge