curl_multibyte: remove access() function wrapper for Windows

- Remove curlx_win32_access() which was a wrapper to use access() in
  Windows.

This is a follow-up to 602fc213, one of two commits which removed
access() calls from the codebase and banned use of the function.

Closes https://github.com/curl/curl/pull/13529

scripts/checksrc.pl

@@ -721,7 +721,7 @@ sub scanfile {
                     v?sprintf|
                     (str|_mbs|_tcs|_wcs)n?cat|
                     LoadLibrary(Ex)?(A|W)?|
-                    access)
+                    _?w?access)
                    \s*\(
                  /x) {
             checkwarn("BANNEDFUNC",