Revert "Fix github app authentication to work with checks API endpoints"

This breaks the anonymous fallback in GitHub when app authentication
is used on repos not having installed the zuul app.

This reverts commit 037f2ce537.

Change-Id: Ie601f8412fd5a646284364d0d0ea08ba32e02c26

releasenotes/notes/app-auth-bd38c5566d8130b3.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    When using GitHub app authentication the fallback to anonymous access
+    was broken for repositories not having installed the zuul app.

zuul/driver/github/githubconnection.py

@@ -34,7 +34,6 @@ import jwt
 import requests
 import github3
 import github3.exceptions
-from github3.session import AppInstallationTokenAuth
 
 from zuul.connection import BaseConnection
 from zuul.lib.gearworker import ZuulGearWorker
@@ -1017,29 +1016,7 @@ class GithubConnection(BaseConnection):
         # if you're authenticating for a project and you're an integration then
         # you need to use the installation specific token.
         if project and self.app_id:
-            # Call get_installation_key to ensure the token gets refresehd in
+            github.login(token=self._get_installation_key(project))
-            # case it's expired.
-            token = self._get_installation_key(project)
-
-            # To set the AppInstallationAuthToken on the github session, we
-            # also need the expiry date, but in the correct ISO format.
-            installation_id = self.installation_map.get(project)
-            _, expiry = self.installation_token_cache.get(installation_id)
-            format_expiry = datetime.datetime.strftime(
-                expiry, "%Y-%m-%dT%H:%M:%SZ"
-            )
-
-            # Usually one should use github.login_as_app_installation() to
-            # authenticate as github app. This method will then request the
-            # access token for the installation or refresh it if necessary and
-            # set the correct class on the github.session.auth attribute to be
-            # identified as github app. As we are alreaedy managing the
-            # installation tokens by ourselves, we just have to set the correct
-            # TokenAuth class on the github.session.auth attribute.
-            github.session.auth = AppInstallationTokenAuth(
-                token, format_expiry
-            )
-
             github._zuul_project = project
             github._zuul_user_id = self.installation_map.get(project)