MAINTAINERS: remove unused NFSD pattern

A series of commits by Christoph Hellwig removed all the files in this
directory, remove the pattern.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>