Remove pyproject.toml from distribution

Remove pyproject.toml from distribution

SQLAlchemy does not want to opt-in to pep-517 at this time
as this would require a custom build backend interface
which we have not built yet, and the standard is not
widely adopted at this time in any case.  Per
[1] [2], the presence of this file indicates a positive opt-in
to pep-517, so it must be omitted from source distributions.

[1] https://pip.pypa.io/en/stable/reference/pip/#pep-517-and-518-support
[2] https://www.python.org/dev/peps/pep-0517/#id5

Fixes: #5207
Change-Id: If8d26a9edf942047920d273d8be778df7a018b3e
(cherry picked from commit f2a817dd7cde50988839750b9c2464675fb4f069)