diff --git a/doc/api/next_api_changes/removals/24923-ES.rst b/doc/api/next_api_changes/removals/24923-ES.rst
new file mode 100644
index 000000000000..fcab80e66e8d
--- /dev/null
+++ b/doc/api/next_api_changes/removals/24923-ES.rst
@@ -0,0 +1,15 @@
+cbook removals
+~~~~~~~~~~~~~~
+
+- ``matplotlib.cbook.MatplotlibDeprecationWarning`` and
+  ``matplotlib.cbook.mplDeprecation`` are removed; use
+  `matplotlib.MatplotlibDeprecationWarning` instead.
+- ``cbook.maxdict``; use the standard library ``functools.lru_cache`` instead.
+
+Groupers from ``get_shared_x_axes`` / ``get_shared_y_axes`` are immutable
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Modifications to the Groupers returned by ``get_shared_x_axes`` and
+``get_shared_y_axes`` are no longer allowed. Note that previously, calling e.g.
+``join()`` would already fail to set up the correct structures for sharing
+axes; use `.Axes.sharex` or `.Axes.sharey` instead.
diff --git a/lib/matplotlib/cbook/__init__.py b/lib/matplotlib/cbook.py
similarity index 98%
rename from lib/matplotlib/cbook/__init__.py
rename to lib/matplotlib/cbook.py
index 1e51f6a834cc..817034e2b042 100644
--- a/lib/matplotlib/cbook/__init__.py
+++ b/lib/matplotlib/cbook.py
@@ -30,19 +30,6 @@
 from matplotlib import _api, _c_internal_utils
 
 
-@_api.caching_module_getattr
-class __getattr__:
-    # module-level deprecations
-    MatplotlibDeprecationWarning = _api.deprecated(
-        "3.6", obj_type="",
-        alternative="matplotlib.MatplotlibDeprecationWarning")(
-        property(lambda self: _api.deprecation.MatplotlibDeprecationWarning))
-    mplDeprecation = _api.deprecated(
-        "3.6", obj_type="",
-        alternative="matplotlib.MatplotlibDeprecationWarning")(
-        property(lambda self: _api.deprecation.MatplotlibDeprecationWarning))
-
-
 def _get_running_interactive_framework():
     """
     Return the interactive framework whose event loop is currently running, if
@@ -578,27 +565,6 @@ def flatten(seq, scalarp=is_scalar_or_string):
             yield from flatten(item, scalarp)
 
 
-@_api.deprecated("3.6", alternative="functools.lru_cache")
-class maxdict(dict):
-    """
-    A dictionary with a maximum size.
-
-    Notes
-    -----
-    This doesn't override all the relevant methods to constrain the size,
-    just ``__setitem__``, so use with caution.
-    """
-
-    def __init__(self, maxsize):
-        super().__init__()
-        self.maxsize = maxsize
-
-    def __setitem__(self, k, v):
-        super().__setitem__(k, v)
-        while len(self) >= self.maxsize:
-            del self[next(iter(self))]
-
-
 class Stack:
     """
     Stack of elements with a movable cursor.
@@ -891,25 +857,17 @@ def __init__(self, grouper):
         self._grouper = grouper
 
     class _GrouperMethodForwarder:
-        def __init__(self, deprecated_kw=None):
-            self._deprecated_kw = deprecated_kw
-
         def __set_name__(self, owner, name):
             wrapped = getattr(Grouper, name)
             forwarder = functools.wraps(wrapped)(
                 lambda self, *args, **kwargs: wrapped(
                     self._grouper, *args, **kwargs))
-            if self._deprecated_kw:
-                forwarder = _api.deprecated(**self._deprecated_kw)(forwarder)
             setattr(owner, name, forwarder)
 
     __contains__ = _GrouperMethodForwarder()
     __iter__ = _GrouperMethodForwarder()
     joined = _GrouperMethodForwarder()
     get_siblings = _GrouperMethodForwarder()
-    clean = _GrouperMethodForwarder(deprecated_kw=dict(since="3.6"))
-    join = _GrouperMethodForwarder(deprecated_kw=dict(since="3.6"))
-    remove = _GrouperMethodForwarder(deprecated_kw=dict(since="3.6"))
 
 
 def simple_linear_interpolation(a, steps):