Revert "python3: bump to 2.6.4"

This reverts commit 23320259, which
causes a lot of build failures. Part of the Python build process tries
to use os.replace(), which is only available since Python 3.3. It
should work if the host-python being built was used, but unfortunately
the system Python ends up being used, causing the build failure.

Fixes:

  http://autobuild.buildroot.net/results/ed95a7ded6bd6c17bd0820b3a96862487b71eb2b/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>