configure: Remove a leftover comment about MSVC C99 support

Support for building with older versions of MSVC (with the
c99wrap/c99conv frontend) was removed in
ce943dd6ac.

Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -4372,12 +4372,6 @@ case "$toolchain" in
         esac
     ;;
     msvc)
-        # Check whether the current MSVC version needs the C99 converter.
-        # From MSVC 2013 (compiler major version 18) onwards, it does actually
-        # support enough of C99 to build ffmpeg. Default to the new
-        # behaviour if the regexp was unable to match anything, since this
-        # successfully parses the version number of existing supported
-        # versions that require the converter (MSVC 2010 and 2012).
         cl_major_ver=$(cl.exe 2>&1 | sed -n 's/.*Version \([[:digit:]]\{1,\}\)\..*/\1/p')
         if [ -z "$cl_major_ver" ] || [ $cl_major_ver -ge 18 ]; then
             cc_default="cl.exe"