Drop UndertowDefaultConfigUpgradeTestCase

UndertowDefaultConfigUpgradeTestCase tests that if we parse and marshal a particular undertow subsystem config file using the WildFly 8 xsd (file presumably matching what we shipped in our standard WildFly 8 config) that the marshaled output will match a config file that uses the current xsd.

This won't work once WFCORE-2704 is fixed because the old config file includes default values (which should be marshaled since they are in the config) while the new file does not. It's basically a bug that parsing these two documents results in the same marshaled output.

This test doesn't serve any purpose any more (we've long since established that a WF 8 config can works in WF 8.1, when the schema changed a lot, and there's a different test that also confirms this) and keeping it around is blocking the important WFCORE-2704 fix.