JIRA: https://jira.spring.io/browse/INT-4054
Fixes GH-1833 (https://github.com/spring-projects/spring-integration/issues/1833)
The `DefaultCandidate` pulled requirement for the `slf4j` dependency via its `Logger` and `LoggerFactory` usage.
* Change `slf4j` to the standard Commons Logging
* Exclude `slf4j` transitive dependencies from `optional` direct dependencies like `reactor` and `json-path`
* Since they are `optional` it is safe to exclude their transitives to force our source code to be free from unexpected dependencies.
Anyway they don't appear in the target application as a SI transitives and end-user is forced to pull them manually to switch on the desired features.
If there is need in the `slf4j` for target application, it must be pulled manually as well.
**Cherry-pick to 4.2.x**
fe5ff04489