Remove vestigial 3DFS support code (re: f88f302c)

Support for the long-dead 3DFS userland versioning file system was
already removed from ksh93 (although I'd overlooked some minor
things), but libast still supported it. This removes that too.

src/lib/libast/include/fs3d.h,
src/lib/libast/man/fs3d.3,
src/lib/libast/misc/fs3d.c:
- Removed.

bin/package,
src/cmd/INIT/package.sh:
- Remove attempted use of removed vpath builtin.

src/cmd/ksh93/*:
- Remove minor 3dfs vestiges.

src/lib/lib{ast,cmd,coshell}/*:
- Remove code supporting 3dfs.

src/cmd/ksh93/include/defs.h

@@ -106,7 +106,6 @@ struct limits
 	int		ngroups_max;	/* maximum number of process groups */
 	unsigned char	posix_version;	/* posix version number */
 	unsigned char	posix_jobcontrol;/* non-zero for job control systems */
-	unsigned char	fs3d;		/* non-zero for 3-d file system */
 };
 
 #ifndef SH_wait_f_defined