qemu-options: stdio is available on win32

Available since commit db418a0a
(October 2011, qemu 1.0)
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-options.hx

@@ -2430,8 +2430,6 @@ Connect to standard input and standard output of the QEMU process.
 exiting QEMU with the key sequence @key{Control-c}. This option is enabled by
 default, use @option{signal=off} to disable it.
 
-@option{stdio} is not available on Windows hosts.
-
 @item -chardev braille ,id=@var{id}
 
 Connect to a local BrlAPI server. @option{braille} does not take any options.