Switch to use flit core since upstream changed.
They also changed the capitalisation under pypi.
The license didn't change but the file was renamed, probably as it wasn't
rst.
(From OE-Core rev: e352680528b18c3cdae26233bef7cddc2771d42d)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
