Remove the warning when a 4.x endpoint receives an event from a 3.x pub, when the event is an interface. 

- Relates to #1834
- Refactored the MessageMetadataRegistry class. 
- Facilitated to remove the un-necessary warning which is displayed when a 3.x endpoint publishes an event which is an interface, where the 3.x endpoint added an __impl to the event type in the header.