Clean the way to get the selectors in a protocol

[jecisc]

This PR add multiple cleanings in the way we can get the selectors in a protocol from a class.

• #selectorsInCategory: was the same than #selectorsInProtocol: so I deprecated it
• #selectorsInProtocol: was removing duplicates but it should never be able to have a duplicates so I removed this extra step that was done with two cast of a collection
• #selectorsInProtocol: was sorting the selectors but no sender was caring about the order. This method is not the place to do sorting. So I removed the sort
• I inlined #methodSelectorsInProtocol: from ClassOrganization to ClassDescription>>#selectorsInProtocol:
• I added missing tests on #selectorsInProtocol: with one tests showing that it was not able to deal with real protocols
• I updated #selectorsInProtocol: to be able to deal with real protocols and not just a protocol name
• I replaced some (class organization protocolNamed: x) methodSelectors to call class selectorsInProtocol: x which is more readable

This cleans a lot of code, reduces some API while making the existing API more robust! This will also help to clean other parts of the system more easily afterward :)