The define is not in our name space and is therefore not protected by
our API promises.
It was only really used by libcurl internals but was mostly erased from
there already in 8aabbf5 (March 2015). This is supposedly the final
death blow to that define from everywhere.
As a side-effect, making sure _MPRINTF_REPLACE is gone and not used, I
made the lib tests in tests/libtest/ use curl_printf.h for its redefine
magic and then subsequently the use of sprintf() got banned in the tests
as well (as it is in libcurl internals) and I then replaced them all
with snprintf().
In the unlikely event that any users is actually using this define and
gets sad by this change, it is very easily copied to the user's own
code.
CURLOPT_DNS_USE_GLOBAL_CACHE broke in commit c43127414d (been
broken since the libcurl 7.29.0 release). While this option has been
documented as deprecated for almost a decade and nobody even reported
this bug, it should remain functional.
Added test case 1512 to verify
