fs: dlm: remove obsolete INBUF define

This patch removes an obsolete define for some length for an temporary
buffer which is not being used anymore. The use of this define is not
necessary anymore since commit 4798cbbf ("fs: dlm: rework receive
handling").

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>