Do not check MultipleObjectsReturned of a get by username as it cannot happen

Usernames are unique by database constraint.

docbow_project/pfwb/management/commands/sendmail.py

@@ -223,10 +223,6 @@ In case of failure the following return value is returned:
                 msg = 'Recipient %r is not an user of the platform' \
                         % email_address
                 content_errors.append(msg)
-            except MultipleObjectsReturned:
-                msg = 'Recipient %r has more than 1 user in the platform' \
-                        % email_address
-                content_errors.append(msg)
         self.filenames = [a for a, b in attachments]
         if not len(attachments):
             content_errors.append('You must send at least one attached file')