This does not work:

SYSROOT_PREPROCESS_FUNCS += " python_sysroot_cleanup"
python_sysroot_cleanup () {
	rm -rf ${SYSROOT_DESTDIR}${libdir}/python${PYTHON_MAJMIN}/test
}

and interestingly and perhaps revealingly, it gives a warning about tab indentation in a python function when its a shell function.

This works:

SYSROOT_PREPROCESS_FUNCS += " py3_sysroot_cleanup"
py3_sysroot_cleanup () {
	rm -rf ${SYSROOT_DESTDIR}${libdir}/python${PYTHON_MAJMIN}/test
}

so it would appear calling variables something with "python_" at the start is problematic.