MAINTAINERS: remove unused nbd.h pattern

Commit 13e71d69 ("nbd: Remove kernel internal header") deleted the
file, remove the pattern.
Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

MAINTAINERS

@@ -7018,7 +7018,6 @@ L:	nbd-general@lists.sourceforge.net
 T:	git git://git.pengutronix.de/git/mpa/linux-nbd.git
 F:	Documentation/blockdev/nbd.txt
 F:	drivers/block/nbd.c
-F:	include/linux/nbd.h
 F:	include/uapi/linux/nbd.h
 
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