Shellcheck correctly reports that we set python_version and never use
it.  This is a leftover from commit f9332757: we used to use
python_version purely to as part of the summary information printed
at the end of a configure run, and that commit changed to printing
the information from meson (which looks up the python version
itself). Remove the unused variable.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20220825150703.4074125-2-peter.maydell@linaro.org