FreeBSD: Cleanup zfs_readdir()

The FreeBSD project's coverity scans found dead code in `zfs_readdir()`.
Also, the comment above `zfs_readdir()` is out of date.

I fixed the comment and deleted all of the dead code, plus additional
dead code that was found upon review.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13924

include/os/freebsd/Makefile.am

@@ -21,7 +21,6 @@ noinst_HEADERS = \
 	%D%/spl/sys/dirent.h \
 	%D%/spl/sys/disp.h \
 	%D%/spl/sys/dkio.h \
-	%D%/spl/sys/extdirent.h \
 	%D%/spl/sys/fcntl.h \
 	%D%/spl/sys/file.h \
 	%D%/spl/sys/freebsd_rwlock.h \

include/os/freebsd/spl/sys/extdirent.h

@@ -1,71 +0,0 @@
-/*
- * CDDL HEADER START
- *
- * The contents of this file are subject to the terms of the
- * Common Development and Distribution License (the "License").
- * You may not use this file except in compliance with the License.
- *
- * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
- * or https://opensource.org/licenses/CDDL-1.0.
- * See the License for the specific language governing permissions
- * and limitations under the License.
- *
- * When distributing Covered Code, include this CDDL HEADER in each
- * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
- * If applicable, add the following below this CDDL HEADER, with the
- * fields enclosed by brackets "[]" replaced with your own identifying
- * information: Portions Copyright [yyyy] [name of copyright owner]
- *
- * CDDL HEADER END
- */
-/*
- * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
- * Use is subject to license terms.
- */
-
-#ifndef _SYS_EXTDIRENT_H
-#define	_SYS_EXTDIRENT_H
-
-#ifdef	__cplusplus
-extern "C" {
-#endif
-
-#include <sys/types.h>
-#include <sys/dirent.h>
-
-/*
- * Extended file-system independent directory entry.  This style of
- * dirent provides additional informational flag bits for each
- * directory entry.  This dirent will be returned instead of the
- * standard dirent if a VOP_READDIR() requests dirent flags via
- * V_RDDIR_ENTFLAGS, and if the file system supports the flags.
- */
-typedef struct edirent {
-	ino64_t		ed_ino;		/* "inode number" of entry */
-	off64_t		ed_off;		/* offset of disk directory entry */
-	uint32_t	ed_eflags;	/* per-entry flags */
-	unsigned short	ed_reclen;	/* length of this record */
-	char		ed_name[1];	/* name of file */
-} edirent_t;
-
-#define	EDIRENT_RECLEN(namelen)	\
-	((offsetof(edirent_t, ed_name[0]) + 1 + (namelen) + 7) & ~ 7)
-#define	EDIRENT_NAMELEN(reclen)	\
-	((reclen) - (offsetof(edirent_t, ed_name[0])))
-
-/*
- * Extended entry flags
- *	Extended entries include a bitfield of extra information
- *	regarding that entry.
- */
-#define	ED_CASE_CONFLICT  0x10  /* Disconsidering case, entry is not unique */
-
-/*
- * Extended flags accessor function
- */
-#define	ED_CASE_CONFLICTS(x)	((x)->ed_eflags & ED_CASE_CONFLICT)
-#ifdef	__cplusplus
-}
-#endif
-
-#endif	/* _SYS_EXTDIRENT_H */

include/os/freebsd/spl/sys/vnode_impl.h

@@ -44,8 +44,6 @@
 #define	IS_DEVVP(vp)	\
 	((vp)->v_type == VCHR || (vp)->v_type == VBLK || (vp)->v_type == VFIFO)
 
-#define	V_XATTRDIR	0x0000	/* attribute unnamed directory */
-
 #define	AV_SCANSTAMP_SZ	32		/* length of anti-virus scanstamp */
 
 /*
@@ -193,11 +191,6 @@
 #define	MODEMASK	07777		/* mode bits plus permission bits */
 #define	PERMMASK	00777		/* permission bits */
 
-/*
- * VOP_ACCESS flags
- */
-#define	V_ACE_MASK	0x1	/* mask represents  NFSv4 ACE permissions */
-
 /*
  * Flags for vnode operations.
  */
@@ -234,12 +227,6 @@ struct taskq;
 #define	CREATE_XATTR_DIR	0x04	/* Create extended attr dir */
 #define	LOOKUP_HAVE_SYSATTR_DIR	0x08	/* Already created virtual GFS dir */
 
-/*
- * Flags for VOP_READDIR
- */
-#define	V_RDDIR_ENTFLAGS	0x01	/* request dirent flags */
-#define	V_RDDIR_ACCFILTER	0x02	/* filter out inaccessible dirents */
-
 /*
  * Public vnode manipulation functions.
  */