Make MarkerStyle immutable

by removing the deprecated public methods that could modify it.

Author: timhoffm

doc/api/next_api_changes/removals/22952-TH.rst

@@ -0,0 +1,5 @@
+MarkerStyle is immutable
+~~~~~~~~~~~~~~~~~~~~~~~~
+The methods ``MarkerStyle.set_fillstyle()`` and ``MarkerStyle.set_marker()``
+have been removed. Create a new `.MarkerStyle` with the respective parameters
+instead.

lib/matplotlib/markers.py

@@ -298,10 +298,6 @@ def is_filled(self):
     def get_fillstyle(self):
         return self._fillstyle
 
-    @_api.deprecated("3.4", alternative="a new marker")
-    def set_fillstyle(self, fillstyle):
-        return self._set_fillstyle(fillstyle)
-
     def _set_fillstyle(self, fillstyle):
         """
         Set the fillstyle.
@@ -327,10 +323,6 @@ def get_capstyle(self):
     def get_marker(self):
         return self._marker
 
-    @_api.deprecated("3.4", alternative="a new marker")
-    def set_marker(self, marker):
-        return self._set_marker(marker)
-
     def _set_marker(self, marker):
         """
         Set the marker.