GH-1739 Removed references to partitionSelectorClass and partitionKeyExtractorClass properties
GH-1739 Removed references to partitionSelectorClass and partitionKeyExtractorClass properties

Resolves #1739

ilayaperumalg/spring-cloud-stream,spring-cloud/spring-cloud-stream,spring-cloud/spring-cloud-stream,spring-cloud/spring-cloud-stream,ilayaperumalg/spring-cloud-stream,garyrussell/spring-cloud-stream,garyrussell/spring-cloud-stream,garyrussell/spring-cloud-stream