Documentation/l1tf: Remove Yonah processors from not vulnerable list

commit 58331136 upstream.

Dave reported, that it's not confirmed that Yonah processors are
unaffected. Remove them from the list.

Reported-by: ave Hansen <dave.hansen@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>