* #18398: gnome: drop Gtk2 support

gnome/configure.ac

gnome/src/Makefile.am

gnome/src/actions.c

gnome/src/config/accountconfigdialog.c

gnome/src/config/accountlistconfigdialog.c

gnome/src/config/addressbook-config.c

gnome/src/config/assistant.c

gnome/src/config/audioconf.c

gnome/src/config/hooks-config.c

gnome/src/config/preferencesdialog.c

gnome/src/config/shortcuts-config.c

gnome/src/config/tlsadvanceddialog.c

gnome/src/contacts/calltree.c

gnome/src/contacts/searchbar.c

gnome/src/gtk2_wrappers.c

gnome/src/gtk2_wrappers.h

gnome/src/main.c

gnome/src/mainwindow.c

gnome/src/messaging/message_tab.c

gnome/src/seekslider.c