MB-9620: drop mccouch notifications on the floor

Because nobody needs them anymore.

We still do vbucket deletions and cleanup of old versions after
compaction as per current agreement. Otherwise ep-engine would stop
working.

Change-Id: I3f0545427e3bad9858ac1e19a8b832f3bbd52cf1
Reviewed-on: http://review.couchbase.org/35933
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>