According to PEP 627, the RECORD file is optional and
doesn't make sense to keep it for system packages. Moreover,
its absence should indicate to other tools like pip that
they should not touch such packages.
Now, we process content of all RECORD files to one
pyproject-record (JSON) which is then used in
%pyproject_save_files. That way, we can remove the original
files in %pyproject_install and keep their content for
later.
PEP 627: https://www.python.org/dev/peps/pep-0627/#optional-record-file
