libceph: remove osdtimeout option entirely

Commit 83aff95e ("libceph: remove 'osdtimeout' option") deprecated
osdtimeout over 8 years ago, but it is still recognized.  Let's remove
it entirely.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>