Revert r66070: "Unload bogus XRC resources in "garbage" unit test."

This change is not needed any longer after r66219 which fixed the real
underlying problem, i.e. that attempting to load an invalid XRC file resulted
in failures when loading all subsequent XRC files.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66220 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775