docs: Delete kconfig docs to fix licensing violation

docs: Delete kconfig docs to fix licensing violation

These 3 Kconfig docs were imported from Linux erroneously.  They are
GPL-2.0-only in Linux, but have no SPDX tag and were placed in such a way to
be included by the blanket statement saying that all RST files are CC-BY-4.0.

We should not be carrying a shadow copy of these docs.  They aren't even wired
into our Sphinx docs, and anyone wanting to refer to Kconfig docs is going to
look at the Linux docs anyway.  These, and more docs can be found at:

  https://www.kernel.org/doc/html/latest/kbuild/

which also have corrections vs the snapshot we took.

Fixes: f80fe2b34f08 ("xen: Update Kconfig to Linux v5.4")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>