ceph: remove Sage's git tree from documentation

Sage's git tree has not been pushed to in years, and it was removed in
commit 3a5ccec ("MAINTAINERS: remove myself as ceph co-maintainer"),
so it is better to remove it in the documentation too.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Documentation/filesystems/ceph.rst

@@ -203,7 +203,6 @@ For more information on Ceph, see the home page at
 
 The Linux kernel client source tree is available at
 	- https://github.com/ceph/ceph-client.git
-	- git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git
 
 and the source for the full system is at
 	https://github.com/ceph/ceph.git