spacemanager: Simplify updateFile method

Alters the logic for updating file records. Rather than
passing the fields to change as arguments to the update method,
the code now simply uses the setter on the File object directly
and saves the result. Besides making the code simpler, it
also allowed a number of update methods to be removed from the
DAO interface - these methods were needed because updateFile
was unable to set fields to null.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6466/