Remove mention of cmp= from next gen docs (#1355)

`attrs.define` and `attrs.field` do not actually accept `cmp=`
anymore, but the docs still discuss them

Author: tjstum

src/attr/_next_gen.py

@@ -76,7 +76,7 @@ def define(
             sensible ``__ne__`` by default, so it *should* be enough to only
             implement ``__eq__`` in most cases).
 
-            Passing True or False` to *init*, *repr*, *eq*, *cmp*, or *hash*
+            Passing True or False` to *init*, *repr*, *eq*, or *hash*
             overrides whatever *auto_detect* would determine.
 
         auto_exc (bool):
@@ -151,10 +151,6 @@ def define(
 
             .. seealso:: `comparison`
 
-        cmp (bool | None):
-            Setting *cmp* is equivalent to setting *eq* and *order* to the same
-            value. Must not be mixed with *eq* or *order*.
-
         unsafe_hash (bool | None):
             If None (default), the ``__hash__`` method is generated according
             how *eq* and *frozen* are set.
@@ -504,12 +500,6 @@ def field(
 
             .. seealso:: `comparison`
 
-        cmp(bool | ~typing.Callable):
-            Setting *cmp* is equivalent to setting *eq* and *order* to the same
-            value. Must not be mixed with *eq* or *order*.
-
-            .. seealso:: `comparison`
-
         hash (bool | None):
             Include this attribute in the generated ``__hash__`` method.  If
             None (default), mirror *eq*'s value.  This is the correct behavior