JIRA: https://jira.spring.io/browse/INT-4437
The `ScatterGatherHandler` overrides a `replyChannel` header for the
scatter message to its internal queue and doesn't reinstate the original
`replyChannel` header when producer a gather result message
* Rebuild gather result message with population a proper `replyChannel`
header from the request message and removing a `gatherResultChannel`
header
**Cherry-pick to 5.0.3 and 4.3.x**
Polishing
64a37381e0