bozo: remove obsolete bnode_Deactivate() prototype

Commit 54eb2485b59550ba42569ed3a8d76211a3a35019 removed the
implementation of bnode_Deactivate(), which had been #ifdef'd out
for a long time, but left the prototype in place. Remove the
obsolete declaration in bosprototypes.h as well.

Change-Id: I323a3f945fcab97d7c4db191192d3ef11482d64e
Reviewed-on: http://gerrit.openafs.org/10868
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>