fs: unexport __kernel_write

This is a very special interface that skips sb_writes protection, and not
used by modules anymore.
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/read_write.c

@@ -522,7 +522,6 @@ ssize_t __kernel_write(struct file *file, const void *buf, size_t count, loff_t
 	inc_syscw(current);
 	return ret;
 }
-EXPORT_SYMBOL(__kernel_write);
 
 ssize_t kernel_write(struct file *file, const void *buf, size_t count,
 			    loff_t *pos)