More minor cosmetic improvements:

More minor cosmetic improvements:

- remove another senseless "extern" keyword that was applied to a
function definition
- change a foo more function signatures from "some_type foo()" to
"some_type foo(void)"
- rewrite another K&R style function definition
- make the type of the "action" function pointer in the KeyWord struct
in src/backend/utils/adt/formatting.c more precise