Remove Python 2.7 support. (#5425)

* remove 2.7 from CI and publishing

* fill out classifiers and also make it not be installed on 3.5

* some minor bumps so that the old deps work on python 3.5

.buildkite/docker-compose.py27.pg94.yaml

@@ -1,21 +0,0 @@
-version: '3.1'
-
-services:
-
-  postgres:
-    image: postgres:9.4
-    environment:
-      POSTGRES_PASSWORD: postgres
-
-  testenv:
-    image: python:2.7
-    depends_on:
-      - postgres
-    env_file: .env
-    environment:
-      SYNAPSE_POSTGRES_HOST: postgres
-      SYNAPSE_POSTGRES_USER: postgres
-      SYNAPSE_POSTGRES_PASSWORD: postgres
-    working_dir: /app
-    volumes:
-      - ..:/app

.buildkite/docker-compose.py27.pg95.yaml

@@ -1,21 +0,0 @@
-version: '3.1'
-
-services:
-
-  postgres:
-    image: postgres:9.5
-    environment:
-      POSTGRES_PASSWORD: postgres
-
-  testenv:
-    image: python:2.7
-    depends_on:
-      - postgres
-    env_file: .env
-    environment:
-      SYNAPSE_POSTGRES_HOST: postgres
-      SYNAPSE_POSTGRES_USER: postgres
-      SYNAPSE_POSTGRES_PASSWORD: postgres
-    working_dir: /app
-    volumes:
-      - ..:/app

.buildkite/pipeline.yml

@@ -48,13 +48,13 @@ steps:
 
   - command:
       - "python -m pip install tox"
-      - "tox -e py27,codecov"
-    label: ":python: 2.7 / SQLite"
+      - "tox -e py35-old,codecov"
+    label: ":python: 3.5 / SQLite / Old Deps"
     env:
       TRIAL_FLAGS: "-j 2"
     plugins:
       - docker#v3.0.1:
-          image: "python:2.7"
+          image: "python:3.5"
           propagate-environment: true
     retry:
       automatic:
@@ -114,57 +114,6 @@ steps:
         - exit_status: 2
           limit: 2
 
-  - command:
-      - "python -m pip install tox"
-      - "tox -e py27-old,codecov"
-    label: ":python: 2.7 / SQLite / Old Deps"
-    env:
-      TRIAL_FLAGS: "-j 2"
-    plugins:
-      - docker#v3.0.1:
-          image: "python:2.7"
-          propagate-environment: true
-    retry:
-      automatic:
-        - exit_status: -1
-          limit: 2
-        - exit_status: 2
-          limit: 2
-
-  - label: ":python: 2.7 / :postgres: 9.4"
-    env:
-      TRIAL_FLAGS: "-j 4"
-    command:
-      - "bash -c 'python -m pip install tox && python -m tox -e py27-postgres,codecov'"
-    plugins:
-      - docker-compose#v2.1.0:
-          run: testenv
-          config:
-            - .buildkite/docker-compose.py27.pg94.yaml
-    retry:
-      automatic:
-        - exit_status: -1
-          limit: 2
-        - exit_status: 2
-          limit: 2
-
-  - label: ":python: 2.7 / :postgres: 9.5"
-    env:
-      TRIAL_FLAGS: "-j 4"
-    command:
-      - "bash -c 'python -m pip install tox && python -m tox -e py27-postgres,codecov'"
-    plugins:
-      - docker-compose#v2.1.0:
-          run: testenv
-          config:
-            - .buildkite/docker-compose.py27.pg95.yaml
-    retry:
-      automatic:
-        - exit_status: -1
-          limit: 2
-        - exit_status: 2
-          limit: 2
-
   - label: ":python: 3.5 / :postgres: 9.4"
     env:
       TRIAL_FLAGS: "-j 4"