chore(linear_algebra/matrix/adjugate): remove unnecessary fin_cases w…

…ith (#16605)

This was the only use of `fin_cases ... with ...` in mathlib, and it wasn't even necessary. Removing it to avoid having to port unused tactic features.



Co-authored-by: Scott Morrison <scott.morrison@gmail.com>

src/linear_algebra/matrix/adjugate.lean

@@ -346,7 +346,7 @@ lemma adjugate_fin_two (A : matrix (fin 2) (fin 2) α) :
 begin
   ext i j,
   rw [adjugate_apply, det_fin_two],
-  fin_cases i with [0, 1]; fin_cases j with [0, 1];
+  fin_cases i; fin_cases j;
   simp only [nat.one_ne_zero, one_mul, fin.one_eq_zero_iff, pi.single_eq_same, zero_mul,
     fin.zero_eq_one_iff, sub_zero, pi.single_eq_of_ne, ne.def, not_false_iff, update_row_self,
     update_row_ne, cons_val_zero, mul_zero, mul_one, zero_sub, cons_val_one, head_cons, of_apply],