[lldb][swift] Re-enable TestSwiftUnknownSelf

This was skipped as it apparently regressed while the swiftTests were
unintentionally disabled. I can't reproduce this failure anymore and it
seems to consistently pass, so let's re-enable it.

Author: Teemperor

lldb/test/API/lang/swift/unknown_self/TestSwiftUnknownSelf.py

@@ -33,7 +33,6 @@ def check_class(self, var_self, broken):
         self.expect("fr v self", substrs=["hello", "world"])
 
 
-    @skipIf #FIXME: This regressed silently due to 2c911bceb06ed376801251bdfd992905a66f276c
     @skipIf(bugnumber="SR-10216", archs=['ppc64le'])
     @swiftTest
     def test_unknown_self_objc_ref(self):