[ticket/11104] Modified core.js ajax calls.

Modified ajax calls in core.js to set option checkbox
to confirm box layout before invoking confirm box.

PHPBB3-11104
[ticket/11104] Reverting changes in js

Due to a jquery error, reverted changes and tracked the
places which caused error.

PHPBB3-11104
[ticket/11104] Made changes requested for pull request.

Added checkbox option to confirm box layout before invoking
method for confirm box. Used 'TOPIC_DELETED' message instead
of a new message. Removed modifications done by overloading
'confirm_box' method and 'delete_post' method.

PHPBB3-11104