extern function cleanup

extern function cleanup

Most of these functions can be static.  A few are unused.
* src/coding.c (encode_string_utf_8, decode_string_utf_8):
Define only if ENABLE_UTF_8_CONVERTER_TEST, as they're
not needed otherwise.
* src/coding.c (encode_string_utf_8, decode_string_utf_8):
* src/data.c (integer_mod):
* src/fns.c (base64_encode_region_1, base64_encode_string_1):
* src/ftfont.c (ftfont_get_fc_charset):
Now static.
* src/sysdep.c (verrprintf): Remove; unused.