Bug 1330474 - Travis: Stop testing against Python 2 (#4675)

Since we've been using Python 3 in production for long enough that we're
confident we won't need to roll back to Python 2.

.travis.yml

@@ -70,25 +70,6 @@ matrix:
       script:
         - python -bb -m pytest tests/selenium/
 
-    # TODO: Remove once we're confident we won't be reverting back to Python 2.
-    - env: python2-smoketest
-      language: python
-      python: '2.7.15'
-      cache:
-        directories:
-          - ${HOME}/venv
-      install:
-        - source ./bin/travis-setup.sh services python_env
-        # Create the test database for `manage.py check --deploy`.
-        - mysql -u root -e 'create database test_treeherder;'
-      script:
-        - pip check
-        - python -3 -bb lints/queuelint.py
-        - flake8 --show-source
-        - isort --check-only --diff --quiet
-        - SITE_URL='https://treeherder.dev' TREEHERDER_DEBUG='False' python -3 -bb ./manage.py check --deploy --fail-level WARNING
-        - python -3 -bb -m pytest tests/ --runslow --ignore=tests/selenium/
-
 notifications:
   email:
     on_success: never

bin/travis-setup.sh

@@ -7,8 +7,6 @@ export BROKER_URL='amqp://guest:guest@localhost:5672//'
 export DATABASE_URL='mysql://root@localhost/test_treeherder'
 export REDIS_URL='redis://localhost:6379'
 export TREEHERDER_DJANGO_SECRET_KEY='secretkey-of-at-50-characters-to-pass-check-deploy'
-# Suppress warnings shown during pytest startup when using `python2 -3` mode.
-export PYTHONWARNINGS='ignore:Overriding __eq__ blocks inheritance of __hash__ in 3.x:DeprecationWarning'
 
 setup_services() {
     echo '-----> Running apt-get update'

setup.cfg

@@ -34,11 +34,6 @@ filterwarnings =
     # however this is expected when running tests since Django collectstatic and yarn build
     # (which create those directories) typically aren't run apart from during deployments.
     ignore:No directory at.*:UserWarning:whitenoise.base
-    # Hide `python2 -3` mode warnings that are false positives
-    ignore:Overriding __eq__ blocks inheritance of __hash__ in 3.x:DeprecationWarning
-    ignore:sys.exc_clear\(\) not supported in 3.x; use except clauses:DeprecationWarning
-    ignore:classic int division:DeprecationWarning:django.db.backends.base.schema
-    ignore:In 3.x, reload\(\) is renamed to imp.reload\(\):DeprecationWarning:django.db.migrations.loader
 markers =
     slow: mark a test as slow.
 xfail_strict = true

treeherder/client/setup.py

@@ -34,8 +34,6 @@ def find_version(*file_paths):
           'Natural Language :: English',
           'Operating System :: OS Independent',
           'Programming Language :: Python',
-          'Programming Language :: Python :: 2',
-          'Programming Language :: Python :: 2.7',
           'Programming Language :: Python :: 3',
           'Programming Language :: Python :: 3.6',
           'Topic :: Software Development :: Libraries :: Python Modules',