Going forward add-ons will be much easier to add/remove. For example, you can remove all references to Photon by deleting the Photon Unity Networking folder.
iTween however is a little messier:
1. Open the PlayMaker/Editor/FsmComponentInspector.cs
2. Comment out #define iTweenPathEditing
3. Delete the PlayMaker/Actions/iTween folder
4. Delete PlayMaker/Include/iTweenFsmEvents.cs
5. Delete the iTween folder
That should completely remove iTween.
I hope to rework this so it works more like the Photon integration. Just delete one folder
However, this is complicated by the Asset Store having no way to remove files from a previous installation... :-/