python_numpy: Fix SRC_URI warnings.

This commit fixes the following warnings:
WARNING: Unable to get checksum for python-numpy SRC_URI entry config.h: file could not be found
WARNING: Unable to get checksum for python-numpy SRC_URI entry numpyconfig.h: file could not be found

Signed-off-by: Elvis Dowson <elvis.dowson@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>