Compilation fix for wxUniv/MSW in wxTLW code dealing with menus.

The code used by WM_INITMENUPOPUP and WM_EXITMENULOOP handlers shouldn't be
used in wxUniv build as it's not used there anyhow and doesn't even compile.

Closes #16039.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76077 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't accept data in unsupported format in wxMSW dnd code.

We wrongly pretended to accept the data in formats which we didn't actually
accept and showed misleading cursors to the user.

Fix this by partially reverting some of the changes of r72668 (see #14697).

Closes #16042.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76078 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775