clean cloud collection terms

On cloud platforms we're expanding and contracting solr nodes using ASGs.
When a new VM instance shows up a new replica is created. When scaled in we detect that and we delete the replica from ZK.

The problem is that, a marker for any replica, even destroyed is still kept in the ZK terms file associated to that collection.

It all works fine until the size of the file /collections/collName/terms/shard1 exceeds 1MB in size (this fills up for us in about 1 year). Then everything blows away as new replicas cannot be registered in ZK.

So the request is the when a replica is deleted to also delete the term associated with it from the terms file.