* examples/book/builder/basic/basic.glade:
* examples/book/builder/derived/derived.glade:
* examples/book/menus/main_menu/examplewindow.cc:
* examples/book/menus_and_toolbars/toolbar.glade:
* examples/book/printing/advanced/examplewindow.cc:
* examples/book/printing/simple/examplewindow.cc: Remove <requires>
elements. They make it difficult to use either e.g. gtk 3.98 or 4.0.
You have to choose one major version or the other.
* examples/book/dialogs/aboutdialog/examplewindow.cc:
Simplify the call to set_logo().