Revert "qemu-options.hx: Update for reboot-timeout parameter"

This reverts commit bbd9e69.

In 20a1922 we allowed reboot-timeout=-1 again, so update the doc
accordingly.

Signed-off-by: Han Han <hhan@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191205024821.245435-1-hhan@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
(cherry picked from commit 8937a39)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qemu-options.hx

@@ -327,8 +327,8 @@ format(true color). The resolution should be supported by the SVGA mode, so
 the recommended is 320x240, 640x480, 800x640.
 
 A timeout could be passed to bios, guest will pause for @var{rb_timeout} ms
-when boot failed, then reboot. If @option{reboot-timeout} is not set,
-guest will not reboot by default. Currently Seabios for X86
+when boot failed, then reboot. If @var{rb_timeout} is '-1', guest will not
+reboot, qemu passes '-1' to bios by default. Currently Seabios for X86
 system support it.
 
 Do strict boot via @option{strict=on} as far as firmware/BIOS