basic_solver adds unexpected evars

[JonasOberhauser]

  Lemma plain_coherence_helper (r s t  : relation actid) : r ∩ s⁻¹ ∪ t ≡ ∅₂ -> irreflexive (s ⨾ r).
  Proof.
    basic_solver 42.

gives me

All the remaining goals are on the shelf:

actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid
actid