the names of the curl_off_t formatting string directives now become
CURL_FORMAT_CURL_OFF_T and CURL_FORMAT_CURL_OFF_TU.
CURL_FMT_OFF_T -> CURL_FORMAT_CURL_OFF_T
CURL_FMT_OFF_TU -> CURL_FORMAT_CURL_OFF_TU
Remove the use of an internal name for the curl_off_t formatting string directives
and use the common one available from the inside and outside of the library.
FORMAT_OFF_T -> CURL_FORMAT_CURL_OFF_T
FORMAT_OFF_TU -> CURL_FORMAT_CURL_OFF_TU