ceph: remove duplicated code in ceph_netfs_issue_read()

When allocating an osd request the libceph.ko will add the
'read_from_replica' flag by default.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>