Revert "fixup! all: Implement server-side OAuth2 protocol."

This reverts commit e925dc0b.
This commit is breaking more than it is fixing. Revert until I have a
working version of this migration.
6 jobs for for_testrunner_3 in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:59:01

passed ERP5.PerformanceTest-Master

00:27:28

failed ERP5.UnitTest-Master

02:13:31

failed ERP5.UnitTest-Master.Medusa

01:52:15

passed SlapOS.Eggs.UnitTest-Master.Python2

00:13:45

passed SlapOS.Eggs.UnitTest-Master.Python3

00:13:55