Don't hard code "open" verb in wxMSW wxLaunchDefaultApplication().

Don't hard code "open" verb in wxMSW wxLaunchDefaultApplication().

Don't choose the verb explicitly and let ShellExecuteEx() choose the default
one. In the vast majority of cases this will do the same thing but if some
file type doesn't have an "open" verb the new version will still open it
correctly using its default verb while the old version failed.

See #10707.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65897 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775