Revert "Add query_label to give each filter a unique label"

This reverts commit 749161e7.

flask_admin/model/filters.py

@@ -72,14 +72,6 @@ class BaseFilter(object):
         """
         raise NotImplemented()
 
-    def query_label(self):
-        """
-            Return a string that can be used in a url to identify this filter.
-            
-            For example u'username_equals'
-        """
-        return '{name}_{operation}'.format(name=self.name, operation=self.operation()).lower().replace(' ', '_')
-
     def __unicode__(self):
         return self.name