gen-casefold-txt.pl and gen-casemap-txt.pl are licensed under GPLv2+, so
they are not touched by this commit.
A lot of *.c files in tests/ don't have a license header.
https://bugzilla.gnome.org/show_bug.cgi?id=776504
Very many testcases, some GLib tools (resource compiler, etc) and
GApplication were calling g_type_init().
Remove those uses, as they are no longer required.
https://bugzilla.gnome.org/show_bug.cgi?id=686161