Bugfix: clicking on a task label now checks the checkbox

[AnSq]

Expected behavior: clicking on a task label will check its checkbox.
Actual behavior: nothing happens.

Setting the for attribute on the label does exactly the same thing as the custom click event listener (toggle the checkbox), so the two methods are cancelling each other out. Simply deleting the event listener solves the issue.

[HelpfulSoft1207]

This was intended because clicking on a collapsible makes it collapse (or expand). What happens if you click on a collapsible task with this change?

[AnSq]

Collapsibles aren't labels, they're spans. Clicking on them is handled by a different event listener on the div.parent-task-header. This PR doesn't change any functionality of collapsible parent tasks. Clicking the label still collapses/expands it without checking the box. (Subtasks do get the new label-clicking behavior though.)