streamlined vsnprintf() check -- now that we fall back to our own printf() version...

streamlined vsnprintf() check -- now that we fall back to our own printf() version anyhow in some cases it doesn't make sense to jump through all these hoops just to avoid it (and, besides, it didn't work anyhow); suppressed vprintf() and vsscanf() checks which results we never used

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@16814 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775