fix(algebra/order): update to lean

The new `not_lt_of_lt` in core is not substitutable for this one because it is in the new algebraic hierarchy and mathlib is still on the old one. But this isn't used anywhere, so I'll just remove it instead of renaming.

Author: digama0

algebra/order.lean

@@ -12,9 +12,6 @@ lemma not_le_of_lt [preorder α] {a b : α} (h : a < b) : ¬ b ≤ a :=
 
 lemma not_lt_of_le [preorder α] {a b : α} (h : a ≤ b) : ¬ b < a
 | hab := not_le_of_gt hab h
- 
-lemma not_lt_of_lt [linear_order α] {a b : α} (h : a < b) : ¬ b < a :=
-lt_asymm h
 
 lemma le_iff_eq_or_lt [partial_order α] {a b : α} : a ≤ b ↔ a = b ∨ a < b :=
 le_iff_lt_or_eq.trans or.comm