We added nox somewhat recently and set it up to mimic existing tox jobs.
This meant adding py27 jobs. Since then (in OpenDev at least) only a
single project has used the py27 job: Bindep. Bindep is dropping support
for python2.7 as the need for it has come to an end. Additionally, nox
doesn't work with python2.7 out of the box due to a virtualenv
dependency that ends up being too new for python2.7 venv creation.
Rather than hack around that let's drop python2.7 job support.
Change-Id: I52c07b01ad173304c19b13a10927fdadf9d84170
378e039dba