* keymap.c: Remove all NS-specific code.

* keymap.c: Remove all NS-specific code.
(where_is_preferred_modifier, Vwhere_is_preferred_modifier): New vars.
(preferred_sequence_p): Rename from ascii_sequence_p; pay attention to
where_is_preferred_modifier, return a different value depending on how
preferred is the binding.
(where_is_internal): Adjust accordingly.
(Fwhere_is_internal): Refresh where_is_preferred_modifier.
Adjust to new preferred_sequence_p.
(syms_of_keymap): Declare `where-is-preferred-modifier'.
* keyboard.c (parse_solitary_modifier): Not static any more.
* keyboard.h (parse_solitary_modifier): Declare.