message: Use existing `witness` function from `expr::prologue`
diff: use crate::{
  circuits::{
  - expr::{prologue::*, Column, ConstantExpr, Variable},
  + expr::{prologue::*, Column, ConstantExpr},
  gate::{CircuitGate, CurrOrNext, JointLookupSpec, LocalPosition, LookupInfo, LookupsUsed},
  wires::COLUMNS,
  },
  @@ -635,12 +635,7 @@ pub fn constraints<F: FftField>(configuration: &LookupConfiguration<F>, d1: D<F>
  .collect()
  };
  - let eval = |pos: LocalPosition| {
  - E::Cell(Variable {
  - col: Column::Witness(pos.column),
  - row: pos.row,
  - })
  - };
  + let eval = |pos: LocalPosition| witness(pos.column, pos.row);
  // This is set up so that on rows that have lookups, chunk will be equal
  // to the product over all lookups `f` in that row of `gamma + f`
  