pythonPackages.django_1_10: drop

Drop django_1_10 ahead of `release-17.09`[1] branch off. Django-1.10
will not be maintained for the entire lifetime of 17.09 so only the 1.8
and 1.11 branches are maintained (both are LTS versions[2]).

[1] https://groups.google.com/forum/#!topic/nix-devel/vILGXXbeCPg
[2] https://www.djangoproject.com/download/