Remove 'vbucket_state_listener'

Unfortunately this feature is non-deterministic especially considering
how the new configuration system works. We can no longer guarantee (and
_should_ no longer guarantee) that <n> configuration updates have
actually been received. Rather the clients (and tests) should only care
about whether a valid configuration has actually been received so that
keys will be mapped to their correct nodes.

Change-Id: I145f4b57b678ffb4a851e9c1526580118f53beda
Reviewed-on: http://review.couchbase.org/38746
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>