No reliable way to remove watcher without interfering others in same watch mode and on same path

It is possible that one node path could be watched more than once by different watchers in same watch mode and same ZooKeeper session. ZOOKEEPER-1910 reported this, but resorted to "checkWatches" to circumvent this. It leaks watches untouched in server side.

I think it might be possible do some tracking works in client to support "removeWatches" without fearing client usages.

Here are some links that lead to this issue:

• ZOOKEEPER-1910: RemoveWatches wrongly removes the watcher if multiple watches exists on a path
• CURATOR-654: DistributedBarrier watcher leak and its pr
• Why removeWatches sends OpCode.checkWatches to the server? from mailing list.
• Drop for watcher from an rust implementation.