Remove code related to long-dead 3DFS research project

This commit gets rid of dead weight related to an obscure early
1990s Bell Labs versioning file system research project called
3DFS, which has not existed for decades and for which I have not
managed to find any evidence that it was ever used outside the lab.

This removes:
- the SHOPT_FS_3D compile option (which was forced on even when 0)
- the obnoxious default alias 2d='set -f;_2d' that turned off your
  globbing and then tried to run a nonexistent _2d command
- undocumented builtins 'vmap' and 'vpath' that only errored out
- a non-functional -V unary operator for the test and [[ commands
- some specific code for Apollo workstations (last made in 1997),
  which was inseparably intertwined with the 3DFS code

(cherry picked from commit 20cdf3709f4fb4e468057b534dcee819b1961fb6)

src/cmd/ksh93/bltins/test.c

@@ -363,23 +363,6 @@ int test_unop(Shell_t *shp,register int op,register const char *arg)
 		return(permission(arg, W_OK));
 	    case 'x':
 		return(permission(arg, X_OK));
-	    case 'V':
-#if SHOPT_FS_3D
-	    {
-		register int offset = staktell();
-		if(stat(arg,&statb)<0 || !S_ISREG(statb.st_mode))
-			return(0);
-		/* add trailing / */
-		stakputs(arg);
-		stakputc('/');
-		stakputc(0);
-		arg = (const char*)stakptr(offset);
-		stakseek(offset);
-		/* FALL THRU */
-	    }
-#else
-		return(0);
-#endif /* SHOPT_FS_3D */
 	    case 'd':
 		return(test_stat(arg,&statb)>=0 && S_ISDIR(statb.st_mode));
 	    case 'c':