configure: remove redundant definition of __USE_MINGW_ANSI_STDIO

No need to define it twice on mingw-w64 >= v3.
Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

configure

@@ -3853,8 +3853,6 @@ probe_libc(){
         if check_${pfx}cpp_condition _mingw.h "__MINGW64_VERSION_MAJOR < 3"; then
             add_compat msvcrt/snprintf.o
             add_cflags "-include $source_path/compat/msvcrt/snprintf.h"
-        else
-            add_${pfx}cppflags -D__USE_MINGW_ANSI_STDIO=1
         fi
         add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
     elif check_${pfx}cpp_condition _mingw.h "defined __MINGW32_VERSION"; then