Removing couple of "buildins" polyglot types

ebook_converter/ebooks/lrf/pylrs/elements.py

@@ -1,7 +1,6 @@
 """
 elements.py -- replacements and helpers for ElementTree
 """
-from ebook_converter.polyglot.builtins import string_or_bytes
 
 
 class ElementWriter(object):
@@ -25,7 +24,7 @@ class ElementWriter(object):
 
     def _writeAttribute(self, f, name, value):
         f.write(' %s="' % str(name))
-        if not isinstance(value, string_or_bytes):
+        if not isinstance(value, (str, bytes)):
             value = str(value)
         value = self._encodeCdata(value)
         value = value.replace('"', '"')