Remove nova cell sync comment

Removed a comment suggesting we use nova-manage db sync --local_cell
when bootstrapping the nova service, since that suggestion has now been
implemented in Kolla. See [1] for more details.

[1]: https://review.opendev.org/c/openstack/kolla/+/902057

Related-Bug: #2045558
Depends-On: Ic64eb51325b3503a14ebab9b9ff2f4d9caec734a
Change-Id: I591f83c4886f5718e36011982c77c0ece6c4cbd7

ansible/roles/nova/tasks/bootstrap_service.yml

 ---
-# TODO(mgoddard): We could use nova-manage db sync --local_cell, otherwise we
-# sync cell0 twice. Should not be harmful without though.
 - name: Running Nova API bootstrap container
   become: true
   vars: