Recent Lean core: if_pos / if_neg deprecated, use ite_eq_left / ite_eq_right

In a recent Lean/Mathlib toolchain, rw [if_pos h] gives a warning: if_pos has been deprecated, use ite_eq_left instead (likewise if_neg becomes ite_eq_right). The new lemmas have the same shape, c → (if c then t else e) = t, so rw [ite_eq_left (by omega)] is a drop-in replacement. Writing _root_.if_pos does not silence the warning. For a hypothesis-free rewrite, simp only [h1, h2, and_self, ↓reduceIte] also works.