code: def remove_tag(self, key, value=None):
          
          if value:
              tags = {key : value}
          else:
              tags = [key]
          status = self.connection.delete_tags([self.id], tags)
          if key in self.tags:
              del self.tags[key]
docs: Remove a tag from this object.  Removing a tag involves a round-trip
          to the EC2 service.
  
          :type key: str
          :param key: The key or name of the tag being stored.
  
          :type value: str
          :param value: An optional value that can be stored with the tag.
                        If a value is provided, it must match the value
                        currently stored in EC2.  If not, the tag will not
                        be removed.  If a value of None is provided, all
                        tags with the specified name will be deleted.
                        NOTE: There is an important distinction between
                        a value of '' and a value of None.