Making title-params no longer required.

In theory, a notification could not need any contextual information
so there's no reason we should make it required.

Now, if the title-params are not provided in the notifcation
definition, it just sets the value to an empty array.

Change-Id: Iba5ce5cc56010101c5e64976c95b37a215dc99fa
Merge "Making title-params no longer required."