Remove support for xkb_layout and xkb_semantics file types

Remove support for xkb_layout and xkb_semantics file types

These are two aggregate file types which are not used anywhere. We
maintain useful-enough backward compatibility in the parser, by treating
them as xkb_keymap. The keymap type allows for all types of components,
so they will still compile fine if they ever come up.

Signed-off-by: Ran Benita <ran234@gmail.com>