Revert "Products.ERP5.ERP5Site: Install erp5_oauth2_{resource,authentication} by default."

This reverts commit 035d099a.
Installing BTs which do not come from produt/ERP5/bootstrap breaks site
creation, except in unit tests.
This commit is very desirable, but not ready, so unfortunately I have
to revert it.
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-Master.Medusa