Revert "[Tizen] Refactor XWalkLauncher for usage of RESET event."

This reverts commit a32332dcc4aa34590e953d84535992e9b823c95a.

This change has several problems, some of which are evident when
Crosswalk is built in debug mode.

 * Lack of a base::AtExitManager in the main function.
 * The dbus::Bus is not properly shut down.
 * Most importantly, the interaction between the D-Bus thread and the
   main thread is incorrect: XWalkLauncher and its dbus::Bus are created
   in the main thread, so many D-Bus methods end up being called there
   instead of in the IO thread. This causes many issues, including the
   crash reported in XWALK-3231.

Reverting this commit causes xwalk-launcher to work again, as otherwise
it would crash almost all the time.

BUG=XWALK-3231
Merge pull request #2761 from rakuco/revert-xwalk-launcher-refactoring

Revert "[Tizen] Refactor XWalkLauncher for usage of RESET event."