Remove special handling for 'disk*.h'

This was originally added so that only one of diskmbr.h or diskpc98.h
was chosen and is no longer needed after PC98's removal.  However, the
special handling was also broken as it effectively prevented the decoding
of ioctls declared in other headers such as <sys/disk.h> or
<sys/disklabel.h>.

lib/libsysdecode/mkioctls

@@ -18,14 +18,12 @@ LC_ALL=C; export LC_ALL
 ioctl_includes=$(
 	cd $includedir
 	find -H -s * -name '*.h' | \
-	egrep -v '(.*disk.*|net/pfvar|net/if_pfsync)\.h' | \
+	egrep -v '(net/pfvar|net/if_pfsync)\.h' | \
 		xargs egrep -l \
 '^#[ 	]*define[ 	]+[A-Za-z_][A-Za-z0-9_]*[ 	]+_IO[^a-z0-9_]' |
 		awk '{printf("#include <%s>\\n", $1)}'
 )
 
-ioctl_includes="$ioctl_includes#include <sys/diskmbr.h>\\n"
-
 awk -v x="$ioctl_includes" 'BEGIN {print x}' |
 	$CPP -nostdinc -I$includedir -dM -DCOMPAT_43TTY - |
 	awk -v ioctl_includes="$ioctl_includes" '