ACPI: delete stale reference in kernel-parameters.txt

Says for acpi=
                        See also Documentation/power/pm.txt, pci=noacpi

but this file does not exist
Reported-by: NAlan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NLen Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -161,8 +161,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			rsdt -- prefer RSDT over (default) XSDT
 			copy_dsdt -- copy DSDT to memory
 
-			See also Documentation/power/pm.txt, pci=noacpi
-
 	acpi_apic_instance=	[ACPI, IOAPIC]
 			Format: <int>
 			2: use 2nd APIC table, if available