Remove the nox-py27 job

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

doc/source/python-jobs.rst

@@ -18,7 +18,6 @@ Python Jobs
 .. zuul:autojob:: tox-bashate
 .. zuul:autojob:: tox-nodejs-npm
 .. zuul:autojob:: nox
-.. zuul:autojob:: nox-py27
 .. zuul:autojob:: nox-py36
 .. zuul:autojob:: nox-py37
 .. zuul:autojob:: nox-py38

playbooks/nox/pre27.yaml

@@ -1,6 +0,0 @@
-- hosts: all
-  tasks:
-    - name: Downgrade virtualenv for python2.7 support
-      # Assume pip is installed in the same relative path as nox
-      # and use that to downgrade virtualenv to a version python2.7 supports.
-      command: "{{ nox_executable | dirname }}/pip install -U virtualenv<20.22.0"

zuul.d/python-jobs.yaml

@@ -396,19 +396,6 @@
     run: playbooks/nox/run.yaml
     pre-run: playbooks/nox/pre.yaml
 
-- job:
-    name: nox-py27
-    parent: nox
-    description: |
-      Run unit tests for a Python project under cPython version 2.7.
-
-      Uses nox with the ``test`` keyword forcing python 2.7.
-    pre-run: playbooks/nox/pre27.yaml
-    vars:
-      nox_keyword: tests
-      nox_force_python: "2.7"
-      python_version: "2.7"
-
 - job:
     name: nox-py36
     parent: nox