[!TARGET_API_MAC_CARBON]: Don't include charset.h or coding.h.

[!TARGET_API_MAC_CARBON]: Don't include charset.h or coding.h.
(QCLIPBOARD): Remove variable.
(syms_of_mac): Don't initialize it.
(Fmac_paste_function, Fmac_cut_function, Fx_selection_exists_p):
Remove functions.
(syms_of_mac): Don't defsubr them.
[TARGET_API_MAC_CARBON] (Qmime_charset, QNFD, QNFKD, QNFC, QNFKC)
(QHFS_plus_D, QHFS_plus_C): New variables.
(syms_of_mac) [TARGET_API_MAC_CARBON]: Initialize them.
[TARGET_API_MAC_CARBON] (get_cfstring_encoding_from_lisp)
(cfstring_create_normalized): New functions.
[TARGET_API_MAC_CARBON] (Fmac_code_convert_string): Likewise.
(syms_of_mac) [TARGET_API_MAC_CARBON]: Defsubr it.