Remove redundant `include' in definition of xkb_symbols "alt-intl-unicode"

Remove redundant `include' in definition of xkb_symbols "alt-intl-unicode"

The definition of:

  xkb_symbols "alt-intl-unicode"

contains:

  include "level3(ralt_switch)"

However, it also contains:

  include "us(intl-unicode)"

which in turn already contains:

  include "level3(ralt_switch)"

Now, an argument can be made that it's more self-documenting to
repeat the directive, but that seems like a fairly weak argument,
especially given that most of "alt-intl-unicode" is inherited
from "intl-unicode" anyway.