DRTVWR-476: Eliminate snprintf_hack::snprintf(). Use MS snprintf().

https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/snprintf-snprintf-snprintf-l-snwprintf-snwprintf-l?view=vs-2017
"Beginning with the UCRT in Visual Studio 2015 and Windows 10, snprintf is no
longer identical to _snprintf. The snprintf function behavior is now C99
standard compliant."

In other words, VS 2015 et ff. snprintf() now promises to nul-terminate the
buffer even in the overflow case, which is what snprintf_hack::snprintf() was
for.

This removal was motivated by ambiguous-call errors generated by VS 2017 for
library snprintf() vs. snprintf_hack::snprintf().