Simplify logic (semantics unchanged) in builtins trap.

IPython/core/builtin_trap.py

@@ -88,13 +88,8 b' class BuiltinTrap(Configurable):'
             self._orig_builtins[key] = orig
             bdict[key] = value
 
-    def remove_builtin(self, key):
+    def remove_builtin(self, key, orig):
         """Remove an added builtin and re-set the original."""
-        try:
-            orig = self._orig_builtins.pop(key)
-        except KeyError:
-            pass
-        else:
             if orig is BuiltinUndefined:
                 del __builtin__.__dict__[key]
             else:
@@ -115,11 +110,9 b' class BuiltinTrap(Configurable):'
     def deactivate(self):
         """Remove any builtins which might have been added by add_builtins, or
         restore overwritten ones to their previous values."""
-        # Note: must iterate over a static keys() list because we'll be
-        # mutating the dict itself
         remove_builtin = self.remove_builtin
-        for key in self._orig_builtins.keys():
-            remove_builtin(key)
+        for key, val in self._orig_builtins.iteritems():
+            remove_builtin(key, val)
         self._orig_builtins.clear()
         self._builtins_added = False
         try: