python3-flit-core: upgrade 3.9.0 -> 3.10.1

python3-flit-core: upgrade 3.9.0 -> 3.10.1

Summary of changes:
- The ``--python`` option can now take the path of a virtualenv folder, as an
  alternative to a Python executable.
- The metadata in packages now has the names of optional dependency groups
  ("extras") normalised, complying with version 2.3 of the metadata standard.
- Fix potential substitution of environment variables into passwords read from
  ``.pypirc`` files.
- A warning is now shown when building packages which specify the old
  ``flit.buildapi`` backend, which should be replaced by
  ``flit_core.buildapi``. It's a good idea to always set a maximum
  version for the build requirement, to protect against changes in
  future major versions of Flit.
- Avoid using the deprecated ``datetime.utcfromtimestamp()``.
- The tests for ``flit_core`` are no longer part of the installed package,
  reducing the size of the wheels.

Remove the -tests package, as the tests are no longer installed.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>