Revert the change to wxGTK build slave configure arguments.

Undo the temporary change of r74975 as it didn't help with fixing the problem
with the failing unit test.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74978 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775