Fix issue sidebar (#32455)

Fix issue sidebar (#32455)

Fix #32453

Major changes:

* revert the `<div class="divider"></div>` in
`templates/repo/issue/branch_selector_field.tmpl` (it was removed by
mistake in ##32444)
* remove incorrect `<div class="inline field">` in
`templates/repo/issue/sidebar/allow_maintainer_edit.tmpl`
* use `gt-ellipsis` to replace the "title" class in the dependency list,
then `.repository .issue-content-right .ui.list .title` could be removed
* remove the "relaxed" from dependency list, then there is no padding,
then `.repository .issue-content-right .ui.list .dependency` could be
removed (`white-space` doesn't have effect either because there is
`gt-ellipsis`)
* remove dead code `.repository .issue-content-right #deadlineForm input
`

The fixed UI should be the same as before.