remove _attach call in writePointer

remove _attach call in writePointer as
it is no longer needed since a stronger
version is done in the native code
when true is passed as the fourth parameter

lib/ref.js

@@ -746,8 +746,12 @@ exports.writeObject = function writeObject (buf, offset, obj) {
 
 exports.writePointer = function writePointer (buf, offset, ptr) {
   debug('writing pointer to buffer', buf, offset, ptr);
+  // Passing true as a fourth parameter does an a stronger
+  // version of attach which ensures ptr is only collected after
+  // the finalizer for buf has run. See
+  // https://github.com/node-ffi-napi/ref-napi/issues/54
+  // for why this is necessary
   exports._writePointer(buf, offset, ptr, true);
-  exports._attach(buf, ptr);
 };
 
 /**