Fix the stale comment on ImpalaServer::RegisterQuery header

Prior to this change, the comment from ImpalaServer::RegisterQuery 
asserts:

"Registers the query exec state with client_request_state_map_ using the
globally unique query_id and add the query id to session state's open 
query list."

This comment is partially inaccurate about the current designs of this 
function since it does not add the query_id to the session state's open 
query list.

Change-Id: If743e718f7322929acb710b36f85978dfbe981bf
Reviewed-on: http://gerrit.cloudera.org:8080/13001
Reviewed-by: Tim Armstrong <[email protected]>
Tested-by: Impala Public Jenkins <[email protected]>
Reviewed-on: https://gerrit.sjc.cloudera.com/c/cdh/impala/+/49575
Reviewed-by: Laszlo Gaal <[email protected]>
Tested-by: Jenkins User <[email protected]>
CDH-Build: Laszlo Gaal <[email protected]>
Quasar-L0: Laszlo Gaal <[email protected]>

be/src/service/impala-server.h

@@ -577,7 +577,7 @@ class ImpalaServer : public ImpalaServiceIf,
       std::shared_ptr<ClientRequestState>* exec_state) WARN_UNUSED_RESULT;
 
   /// Registers the query exec state with client_request_state_map_ using the
-  /// globally unique query_id and add the query id to session state's open query list.
+  /// globally unique query_id.
   /// The caller must have checked out the session state.
   Status RegisterQuery(std::shared_ptr<SessionState> session_state,
       const std::shared_ptr<ClientRequestState>& exec_state) WARN_UNUSED_RESULT;