Revert "[vm/win] Use wide-character api for local hostname on Windows."

This reverts commit 7bdbc05 as it makes dart crash on Windows 7 and earlier.

Bug: flutter/flutter#130554
Change-Id: I61224ea89aec968465e2bc4fa1dafe0eca215677
TEST=ci
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/320620
Auto-Submit: Alexander Aprelev <aam@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
Commit-Queue: Siva Annamalai <asiva@google.com>

runtime/bin/platform_win.cc

@@ -218,14 +218,7 @@ bool Platform::LocalHostname(char* buffer, intptr_t buffer_length) {
   if (!SocketBase::Initialize()) {
     return false;
   }
-  // 256 is max length per https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-gethostnamew#remarks
-  const int HOSTNAME_MAXLENGTH = 256;
-  wchar_t hostname_w[HOSTNAME_MAXLENGTH];
-  if (GetHostNameW(hostname_w, HOSTNAME_MAXLENGTH) != 0) {
-    return false;
-  }
-  return WideCharToMultiByte(CP_UTF8, 0, hostname_w, -1, buffer, buffer_length,
-                             nullptr, nullptr) != 0;
+  return gethostname(buffer, buffer_length) == 0;
 #endif
 }