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/lib/libast/misc/setenviron.c

@@ -23,8 +23,6 @@
 
 #include "intercepts.h"
 
-#include <fs3d.h>
-
 /*
  * put name=value in the environment
  * pointer to value returned
@@ -75,15 +73,6 @@ setenviron(const char* akey)
 			n = INCREMENT;
 		if (!p || (last - p + 1) < n)
 		{
-			if (!p && fs3d(FS3D_TEST))
-			{
-				/*
-				 * kick 3d initialization
-				 */
-
-				close(open(".", O_RDONLY|O_cloexec));
-				v = environ;
-			}
 			if (!(p = newof(p, char*, n, 0)))
 				return 0;
 			last = p + n - 1;