Removed obsolete error.
Rewrote WithGiven methods to use WithoutGiven methods
Merge branch 'master' of https://github.com/sebasguts/CategoriesForHomalg

* 'master' of https://github.com/sebasguts/CategoriesForHomalg:
  Rewrote WithGiven methods to use WithoutGiven methods
  Removed obsolete error.