chore: delete deprecated algebraic structure files (#16836)

Based on a comparison with 32de3f6 these six files have not been substantially changed for over a year.



Co-authored-by: Kim Morrison <kim@tqft.net>

Author: Parcly-Taxel

Mathlib.lean

@@ -3086,19 +3086,13 @@ import Mathlib.Deprecated.Cardinal.Finite
 import Mathlib.Deprecated.Cardinal.PartENat
 import Mathlib.Deprecated.Combinator
 import Mathlib.Deprecated.Equiv
-import Mathlib.Deprecated.Group
 import Mathlib.Deprecated.HashMap
 import Mathlib.Deprecated.LazyList
 import Mathlib.Deprecated.Logic
 import Mathlib.Deprecated.MinMax
 import Mathlib.Deprecated.NatLemmas
 import Mathlib.Deprecated.Order
 import Mathlib.Deprecated.RelClasses
-import Mathlib.Deprecated.Ring
-import Mathlib.Deprecated.Subfield
-import Mathlib.Deprecated.Subgroup
-import Mathlib.Deprecated.Submonoid
-import Mathlib.Deprecated.Subring
 import Mathlib.Dynamics.BirkhoffSum.Average
 import Mathlib.Dynamics.BirkhoffSum.Basic
 import Mathlib.Dynamics.BirkhoffSum.NormedSpace