Remove commons-logging from classpath

[burkedavison]

Pubsub-stream-binder and logging integration tests produce this message:

Standard Commons Logging discovery in action with spring-jcl: please remove commons-logging.jar from classpath in order to avoid potential conflicts

(Example log)

This dependency is brought in via spring-cloud-gcp-logging's com.google.cloud:google-cloud-logging-logback dependency,
and spring-cloud-gcp-pubsub's com.google.cloud:google-cloud-pubsub dependency.

[zhumin8]

Adding a note: we should remove commons-logging from classpath for all artifacts published via SCGCP

[zhumin8]

fixed by #2407, and remaining cleanup after googleapis/google-http-java-client#1905 has been released captured in #2415. Thus closing this one.