fixed several places that unnecessarily take a reference to the event context

fixed several places that unnecessarily take a reference to the event context

These references were triggering the ambiguous talloc_free errors from
the recent talloc changes when the server is run using the 'standard'
process model instead of the 'single' process model. I am aiming to
move the build farm to use the 'standard' process model soon, as part
of an effort to make our test environment better match the real
deployment of Samba4.

The references are not needed as the way that the event context is
used is as the 'top parent', so when the event context is freed then
all of the structures that were taking a reference to the event
context were actually freed as well, thus making the references
redundent.