Get rid of more uses of CellNucleus#send methods

Depending on the situation the code is either deleted, ported to CellStub,
or ported to CellEndpoint.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/6757/