This reverts commit a47ff0dd4a.
Since this merged, a global-requirements pin to keep networkx <2.0 has
also merged. The plan is:
1. revert our 2.0 support and
1a. take the <2.0 pin from global requirements
2. figure out how to use constraints properly in our testing
3. restore this, with a depends-on for a 2.0 bump in requirements
(which will self-test, see 3.)
4. when other projects are ready for a global 2.0 bump, merge
in a controlled fashion
This reverts the 2.0 support, and adds the pin for networkx <2.0
Change-Id: I18f6a1115da779581245e3dd423fd90516974a33
06b5ce4573