qnx4 wrte support has never been fully implement, is broken since the dawn
of time and hasn't been actively developed since before git history
started.

Instead of letting it further bitrot and complicate API transition (like
the new truncate code) remove it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Cc: Anders Larsen <al@alarsen.net>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>