clean vendorized remoto in debian/rules

Based on [vendor.py:51](https://github.com/ceph/ceph-deploy/blob/master/vendor.py#L51), if the clone of the vendorized library already exists in the source tree, it will not be re-cloned, even if its version in [setup.py:22](https://github.com/ceph/ceph-deploy/blob/master/setup.py#L22) is bumped.

A full solution to this problem would be to compare the version of the available clone with the requirements in vendor_library(), this patch adds `rm -rf remoto` to the debian/rules `clean` target to reduce impact of this problem until a full solution is implemented.