lockd: Remove dead code from fs/lockd/xdr4.c

lockd: Remove dead code from fs/lockd/xdr4.c

Now that all NLMv4 server-side procedures use XDR encoder and
decoder functions generated by xdrgen, the hand-written code in
fs/lockd/xdr4.c is no longer needed. This file contained the
original XDR processing logic that has been systematically
replaced throughout this series.

Remove the file and its Makefile reference to eliminate the
dead code. The helper function nlm4svc_set_file_lock_range()
is still needed by the generated code, so move it to xdr4.h
as an inline function where it remains accessible.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>