Document complete removal of Moxi support

From Artem:

Moxi support is completely removed in MadHatter. The only thing that is left is ability to manually remove moxi port from the bucket created in earlier release, so MadHatter node will be able to rebalance in.

1. MadHatter clusters do not allow buckets with moxi ports.

2. It is not possible to add pre-MadHatter node to MadHatter cluster

3. It is possible to add MadHatter node to pre-MadHatter cluster with the bucket that has

4. moxi port, but the rebalance will be not possible until the port is unset.

5. Port is removed via CLI

The following pages (at least) need to be updated to remove moxi-related info:

https://docs.couchbase.com/server/6.5/cli/cbcli/couchbase-cli-bucket-edit.html

https://docs.couchbase.com/server/6.5/install/upgrade.html

https://docs.couchbase.com/server/6.5/release-notes/relnotes.html

https://docs.couchbase.com/server/6.5/install/install-ports.html