staging/lustre: Remove ns_is_server()

Since the code we have is Lustre-client only, this function
always returns 0, so drop it and amend all the callsites to
drop dead code.
One of the places also sets LDLM_FL_NS_SRV to indicate a lock
is in a server namespace. This too cannot happen in this code,
so drop all such checks as well.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>