UAPI: Remove empty non-UAPI Kbuild files

Remove non-UAPI Kbuild files that have become empty as a result of UAPI
disintegration.  They used to have only header-y lines in them and those have
now moved to the Kbuild files in the corresponding uapi/ directories.

Possibly these should not be removed but rather have a comment inserted to say
they are intentionally left blank.  This would make it easier to add generated
header lines in future without having to restore the infrastructure.

Note that at this point not all the UAPI disintegration parts have been merged,
so it is likely that more empty Kbuild files will turn up.

It is probably necessary to make the files non-empty to prevent the patch
program from automatically deleting them when it reduces them to nothing.
Signed-off-by: David Howells <dhowells@redhat.com>

include/Kbuild

 # Top-level Makefile calls into asm-$(ARCH)
 # List only non-arch directories below
 
-header-y += asm-generic/
 header-y += linux/
 header-y += sound/
-header-y += mtd/
 header-y += rdma/
 header-y += video/
-header-y += drm/
-header-y += xen/
 header-y += scsi/

include/linux/Kbuild

-header-y += byteorder/
-header-y += can/
-header-y += caif/
 header-y += dvb/
 header-y += hdlc/
 header-y += hsi/
-header-y += isdn/
-header-y += mmc/
-header-y += nfsd/
 header-y += raid/
-header-y += spi/
-header-y += sunrpc/
-header-y += tc_act/
-header-y += tc_ematch/
-header-y += netfilter/
-header-y += netfilter_arp/
-header-y += netfilter_bridge/
-header-y += netfilter_ipv4/
-header-y += netfilter_ipv6/
 header-y += usb/
-header-y += wimax/

include/linux/netfilter/Kbuild

-header-y += ipset/