Fix eptid key encoding for python 3

In python3 shelve wants strings for keys, but we were forcing bytes for
some reason.

src/saml2/eptid.py

@@ -42,6 +42,8 @@ class Eptid(object):
         return self._db[key]
 
     def __setitem__(self, key, value):
+        if six.PY3 and isinstance(key, six.binary_type):
+            key = key.decode('utf-8')
         self._db[key] = value
 
     def get(self, idp, sp, *args):

src/saml2/ident.py

@@ -111,9 +111,6 @@ class IdentDB(object):
         :param ident: user identifier
         :param name_id: NameID instance
         """
-        if isinstance(ident, six.string_types):
-            ident = ident.encode("utf-8")
-
         # One user may have more than one NameID defined
         try:
             val = self.db[ident].split(" ")