Clean up unused routes

I tried to clean up the routes as mentioned in #14584 (closed)

I used the following script and manually verified the changes: https://gist.github.com/strzibny/4ccbda7dcf67ef6719dcb047014e1ea7

After this patch, the script still gives me the following routes:

Unused routes (7): oauth/authorizations#show doorkeeper/tokens#create doorkeeper/tokens#revoke oauth/applications#edit oauth/applications#show doorkeeper/token_info#show omniauth_callbacks#(?-mix:(?!))

Here is a relevant code from doorkeeper on drawing these routes: https://github.com/doorkeeper-gem/doorkeeper/blob/5ea4575863781940fe6996692c6b41f2ad71d90e/lib/doorkeeper/rails/routes.rb#L25