packaging: Removed obsolete add_fn_db_get_async_tasks_function.sql

This patch removes an obsolete code loading into the DB during
upgrade flows.

Change-Id: Ic0ca20ff2da1bdf8f6037e877b3697b7af8443c2
Bug-Url: https://bugzilla.redhat.com/951092
Signed-off-by: Alex Lourie <alourie@redhat.com>