Deprecate long --test module/testcase syntax

[mattias-p]

After #333 you can specify the shorter --test delegation01 or the longer --test Delegation/delegation01 to express the exact same thing. With this improvement in place we should consider deprecating the long format because it adds complexity in implementation and documentation and it doesn't add any value.

Perhaps the long format would make sense if we were to move to a different naming convention for the test cases but I haven't heard anyone questioning that naming convention in quite a few years.