Prepare to upgrade to django-oauth-toolkit (module name oauth2_provider) 1.3.2 concurrently with the Django 2.2 upgrade (versions after 1.1.3 dropped support for Django 1.11). Key points:
* We can stop using a commit hash since versions 1.3.0 through 1.3.2 have been released since that commit.
* The validator in oauth_dispatch migration 0002 has been removed from DOT, but the whole table was removed in migration 0004 anyway. Newer DOT versions moved where redirect URI validation happens so it's no longer needed here.
* DOT 1.3.0 squashed its original 6 migrations and immediately deleted them. This required some changes in oauth_dispatch migrations 0006 and 0007 to deal with either numbering system.
When deploying to stage and production, we'll need to delete the history for oauth2_provider migrations 0002-0006 first (the new squashed 0001 migration has the same name as the original 0001). The deployment with DOT 1.3.2 will add a new 0002 migration which should then apply cleanly on the existing database state.
Should resolve https://openedx.atlassian.net/browse/BOM-1456 .