obsolete: update tests to use obsolete options The obsolete._enabled flag has become a config option. This updates all but one of the tests to use the minimal number of flags necessary for them to pass. For most tests this is just 'createmarkers', for a couple tests it's 'allowunstable', and for even fewer it's 'exchange'.

obsolete: prevent options from being used without createmarkers exchange and allowunstable should only be enabled if createmarkers is enabled, so check for that and raise an exception if that's not the case.