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/features/poll

@@ -68,7 +68,6 @@ tst	pipe_socketpair note{ use socketpair() for peekable pipe() }end execute{
 }end
 tst	socketpair_devfd note{ /dev/fd/N handles socketpair() }end execute{
 	#include <ast.h>
-	#include <fs3d.h>
 	#include <sys/types.h>
 	#include <sys/socket.h>
 	int main()
@@ -76,7 +75,6 @@ tst	socketpair_devfd note{ /dev/fd/N handles socketpair() }end execute{
 		int		devfd;
 		int		n;
 		int		sfd[2];
-		fs3d(FS3D_OFF);
 		close(0);
 		open("/dev/null", O_RDONLY);
 		if ((n = open("/dev/fd/0", O_RDONLY)) < 0)