remove wrong pickle register in type D

src/sage/combinat/root_system/type_D.py

@@ -10,6 +10,7 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 from . import ambient_space
+from sage.misc.persist import register_unpickle_override
 
 
 class AmbientSpace(ambient_space.AmbientSpace):
@@ -116,11 +117,6 @@ def fundamental_weight(self, i):
             return self.sum(self.monomial(j) for j in range(i))
 
 
-from sage.misc.persist import register_unpickle_override
-register_unpickle_override('sage.combinat.root_system.type_A',
-                           'ambient_space',
-                           AmbientSpace)
-
 from sage.misc.cachefunc import cached_method
 from .cartan_type import CartanType_standard_finite, CartanType_simply_laced, CartanType_simple
 
@@ -356,6 +352,5 @@ def ascii_art(self, label=None, node=None):
 
 
 # For unpickling backward compatibility (Sage <= 4.1)
-from sage.misc.persist import register_unpickle_override
 register_unpickle_override('sage.combinat.root_system.type_D',
                            'ambient_space', AmbientSpace)