ACPI: docs: Drop useless DSDT override documentation

Because https://01.org/linux-acpi web site has become permanently
inaccessible, the "Overriding DSDT" document in the kernel tree
pointing to it as the main source of information is useless (and
the config option name mentioned by it is incorrect), so drop it
and drop the pointer to it from the ACPI Kconfig.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/admin-guide/acpi/dsdt-override.rst

-.. SPDX-License-Identifier: GPL-2.0
-
-===============
-Overriding DSDT
-===============
-
-Linux supports a method of overriding the BIOS DSDT:
-
-CONFIG_ACPI_CUSTOM_DSDT - builds the image into the kernel.
-
-When to use this method is described in detail on the
-Linux/ACPI home page:
-https://01.org/linux-acpi/documentation/overriding-dsdt

drivers/acpi/Kconfig

@@ -347,7 +347,6 @@ config ACPI_CUSTOM_DSDT_FILE
 	depends on !STANDALONE
 	help
 	  This option supports a custom DSDT by linking it into the kernel.
-	  See Documentation/admin-guide/acpi/dsdt-override.rst
 
 	  Enter the full path name to the file which includes the AmlCode
 	  or dsdt_aml_code declaration.