emulation: Drop ISO-2022 support

https://bugzilla.gnome.org/show_bug.cgi?id=732586
emulation: Drop support for default/UTF-8 character set escape sequences

https://bugzilla.gnome.org/show_bug.cgi?id=731208
emulation: Save/restore alternate charset

https://bugzilla.gnome.org/show_bug.cgi?id=731205