configure: Remove unused python_version variable

Shellcheck correctly reports that we set python_version and never use
it.  This is a leftover from commit f9332757898a7: 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

configure

@@ -1112,9 +1112,6 @@ if ! $python -c 'import sys; sys.exit(sys.version_info < (3,6))'; then
       "Use --python=/path/to/python to specify a supported Python."
 fi
 
-# Preserve python version since some functionality is dependent on it
-python_version=$($python -c 'import sys; print("%d.%d.%d" % (sys.version_info[0], sys.version_info[1], sys.version_info[2]))' 2>/dev/null)
-
 # Suppress writing compiled files
 python="$python -B"