Remove unused variable.

The file descriptor arg to child_process._forkChild() is not used any more.
Remove it, avoids future confusion.

src/node.js

@@ -416,8 +416,7 @@
     // If we were spawned with env NODE_CHANNEL_FD then load that up and
     // start parsing data from that stream.
     if (process.env.NODE_CHANNEL_FD) {
-      var fd = parseInt(process.env.NODE_CHANNEL_FD);
+      assert(parseInt(process.env.NODE_CHANNEL_FD) >= 0);
-      assert(fd >= 0);
       var cp = NativeModule.require('child_process');
 
       // Load tcp_wrap to avoid situation where we might immediately receive
@@ -425,7 +424,7 @@
       // FIXME is this really necessary?
       process.binding('tcp_wrap')
 
-      cp._forkChild(fd);
+      cp._forkChild();
       assert(process.send);
     }
   }