DataNodeId removeConnection(String connectionId) {
      availableConnections.remove(connectionId);
      poolCount--;
      return dataNodeId;
    }
Remove a connection managed by this manager. This connection id could be either a checked out connection or a
connection that was previously available to be checked out.
@param connectionId the connection id of the connection.
@return {@link DataNodeId} associated with this manager and this connection.
ambry-network/src/main/java/com/github/ambry/network/ConnectionTracker.java