Remove ckan.lib.helpers.get_action()

This function is a bad idea because action functions that raise exceptions crash templates (which cannot catch exceptions). See http://lists.okfn.org/pipermail/ckan-dev/2013-August/005609.html

Instead, if you want to make an action available to a template, wrap each individual action in a template helper function that deals with any exceptions raised appropriately.

(Template helper functions should never raise exceptions.)

If `ckan.lib.helpers.get_action()` has been in a CKAN release already then it should be deprecated for one release, if not we can just delete it right away.