Revert "SessionStore: replace password with PASSWORD_HIDDEN when storing in db"

This reverts commit 53f126082a, which
broke user authentication.

Fixes issue #4016.
Reopens issue #3421.

src/node/db/SessionStore.js

@@ -38,11 +38,6 @@ SessionStore.prototype.get = function(sid, fn) {
 SessionStore.prototype.set = function(sid, sess, fn) {
   messageLogger.debug('SET ' + sid);
 
-  // don't store passwords in DB
-  if (sess.user && sess.user.password) {
-    sess.user.password = "PASSWORD_HIDDEN";
-  }
-
   db.set("sessionstorage:" + sid, sess);
   if (fn) {
     process.nextTick(fn);