Remove obsolete "NotifyTest" feed story

Summary: Depends on D19864. Ref T13222. See PHI996. This is no longer used by anything, so get rid of it.

Test Plan: Grepped; viewed a feed with these stories in it to make sure nothing crashed/exploded.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13222

Differential Revision: https://secure.phabricator.com/D19865