Are you talking about the Softkey (right) or the in all the other apps. I'm assuming that you already uninstalled the app.
Take a look at
this thread.
If you want to set the soft keys back to default. Use a registry editing program the 113 key should look like this
* HKEY_CURRENT_USER\Software\Microsoft\Today\Keys\11 3\(Default) = Contacts
* HKEY_CURRENT_USER\Software\Microsoft\Today\Keys\11 3\Open = \Windows\AppButtons\Contacts.Lnk