JIRA: https://jira.spring.io/browse/INT-4485
The `IntegrationFlowBeanPostProcessor` performs extra bean registration
for the `IntegrationComponentSpec.get()` result.
Essentially it is going to be the same object in the end, but during
bean registration phase we end up with names conflict.
* Remove an explicit `registerComponent()` for the
`IntegrationComponentSpec.get()`
* Modify `CorrelationHandlerTests` for all possible usage for the
`MessageChannelSpec`, which is essentially a `FactoryBean`
**Cherry-pick to 5.0.x**
da53ed6838