ceph: remove "Debugging hook" from ceph_fill_trace

Keeping around commented out code is just asking for it to bitrot and
makes viewing the code under cscope more confusing.  If
we really need this, then we can revert this patch and put it under a
Kconfig option.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>