Remove ring id optimization in riak_kv_ensembles

Since the ring does not change when bucket types are activated we remove
the check for a changing ring id that was supposed to prevent
unnecessary work. Leaving the optimization in would require changing
riak_core to trigger on cluster metadata changes in addition to ring
changes. This change thus prevents us from having to change riak_core
at the expense of some extra work to check if the ensembles have changed
when they probably haven't.