Use normal event loop in GUI test program.

Use normal event loop in GUI test program.

Don't create an event loop manually, let the port-specific code do it and run
it as usual in the GUI unit tests.

This has several advantages:
 - No need to manage the event loop manually in the test.
 - No need for Mac-specific code in the test itself.
 - Code being tested runs in the same context as in a normal GUI program,
   which is especially important for event-loop related tests under wxOSX as
   the main event loop is special there.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74334 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775