removed (hopefully) dead code

Cython/Compiler/PyrexTypes.py

@@ -379,14 +379,8 @@ class BuiltinObjectType(PyObjectType):
     base_type = None
     module_name = '__builtin__'
 
-    alternative_name = None # used for str/bytes duality
-
     def __init__(self, name, cname):
         self.name = name
-        if name == 'str':
-            self.alternative_name = 'bytes'
-        elif name == 'bytes':
-            self.alternative_name = 'str'
         self.cname = cname
         self.typeptr_cname = "&" + cname
                                  
@@ -403,9 +397,7 @@ class BuiltinObjectType(PyObjectType):
         
     def assignable_from(self, src_type):
         if isinstance(src_type, BuiltinObjectType):
-            return src_type.name == self.name or (
-                src_type.name == self.alternative_name and
-                src_type.name is not None)
+            return src_type.name == self.name
         elif src_type.is_extension_type:
             return (src_type.module_name == '__builtin__' and
                     src_type.name == self.name)