Library internal only C preprocessor macros FORMAT_OFF_T and FORMAT_OFF_TU

remain in use as internal curl_off_t print formatting strings for the internal
*printf functions which still cannot handle print formatting string directives
such as "I64d", "I64u", and others available on MSVC, MinGW, Intel's ICC, and
other DOS/Windows compilers.

This reverts previous commit part which did:

FORMAT_OFF_T  -> CURL_FORMAT_CURL_OFF_T
FORMAT_OFF_TU -> CURL_FORMAT_CURL_OFF_TU