Unsurprisingly, meson does not support the ratbag keyword argument. Though it
should, because we're great. But anyway, this lead to the argument being
ignored which means it didn't get an 'input' argument, which means that
libratbag-version.h.in was ignored. And since it all works anyway (Behold! The
magic! Ooooh! Aaaah!) we can just drop that file.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>