Get rid of sessionstore component in Torbutton
There is no usecase anymore for our tbSessionStore.js. https://bugzilla.mozilla.org/show_bug.cgi?id=944557 made sure that there is nothing written to disk in Private Browsing Mode in the first place and if one disables disk blocking there is no need for us to strip information (apart from the fact that this is not working anymore either as |subject| in the notification is |null|.