[DOC] Add missing link to handlebars.helpers.input in Ember.Checkbox.
Revert "Docs: Fix link in handlebars text field API"

This reverts commit c9be7cf1b968286dd507736076ff70219ad7ddee.
Merge pull request #3764 from abuiles/add_link_to_handlebars_checkbox

[DOC] Add missing link to handlebars.helpers.input in Ember.Checkbox.