Can you trade without a merchant?

The item you are referring to was the "Cauldron of Jordan" which allowed you to vendor your items without going to town. This feature was removed during beta, because the developers felt that it took away from the experience of going to town. They also felt that since the town portal feature was activated, and therefore provided an easy way to get back to town, the Cauldron was no longer necessary.

Here is the blue post by Jay Wilson explaining the change:

"They were implemented to allow for salvaging and selling items when there was no quick and easy way to return to town. Now that the Stone of Recall exists, we found that keeping the Cauldron and Cube in the game detracted from the benefits of returning to town to sell items, salvage, craft, and interact with the townsfolk. It’s a good idea to break up combat so that players have a moment to evaluate their gear and crafting options before venturing back out. In addition, we’ve decided to just call it what it is and the Stone of Recall is now Town Portal, and is integrated directly onto the skill bar UI."

No, that was removed, in any of the cases you have to use the portal, go back to town and sell it. You can go back using the portal again.