python: remove obsolete samba_external directory
It seems this was once meant to contain third-party python libraries
that we hoped would already be on the system, of which there was only
ever one candidate, dnspython, which we moved then stopped bundling
years ago.
The ancestor of this directory, 'source4/scripting/python/samba_external/'
was unused since
4bbc3ff037026c72f3249f59c1b5af69a6ad6d69 (2010) and
the current location has never done anything.
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jeremy Allison <jra@samba.org>