Remove inheritance_diagram.py.

Since b107f0ab87fac9f8, we are using inheritance_diagram.py provided
by Sphinx ≥ 0.6.
Merge pull request #659 from mitya57/master

Remove inheritance_diagram.py
enh: update internal prov to latest version of external library
Merge pull request #664 from satra/enh/provupdate

enh: update internal prov to latest version of external library