Remove: officially mark Vista as no longer supported (#11531)

It is very likely Vista hasn't been working for years, but the
amount of users that use an OS that has been EoL for over 11 years
is very small, so reports happen rarely.

src/sound/win32_s.cpp

@@ -70,7 +70,7 @@ const char *SoundDriver_Win32::Start(const StringList &parm)
 	wfex.nAvgBytesPerSec = wfex.nSamplesPerSec * wfex.nBlockAlign;
 
 	/* Limit buffer size to prevent overflows. */
-	_bufsize = GetDriverParamInt(parm, "bufsize", IsWindowsVistaOrGreater() ? 8192 : 4096);
+	_bufsize = GetDriverParamInt(parm, "bufsize", 8192);
 	_bufsize = std::min<int>(_bufsize, UINT16_MAX);
 
 	try {