Remove useless attachToDocument usage in spec/frontend/vue_shared

What does this MR do?

As described in &2419 (closed), cleans up our Jest tests from unnecessary attachToDocument usage

Involved specs

• spec/frontend/vue_shared/components/paginated_list_spec.js
• spec/frontend/vue_shared/components/resizable_chart_container_spec.js
• spec/frontend/vue_shared/components/sidebar/labels_select/base_spec.js
• spec/frontend/vue_shared/components/sidebar/labels_select/dropdown_value_spec.js
• spec/frontend/vue_shared/components/time_ago_tooltip_spec.js
• spec/frontend/vue_shared/components/user_avatar/user_avatar_link_spec.js
• spec/frontend/vue_shared/components/user_popover/user_popover_spec.js
• spec/frontend/vue_shared/components/notes/system_note_spec.js
• spec/frontend/vue_shared/components/changed_file_icon_spec.js
• spec/frontend/vue_shared/components/clipboard_button_spec.js
• spec/frontend/vue_shared/components/commit_spec.js
• spec/frontend/vue_shared/components/issue/issue_assignees_spec.js
• spec/frontend/vue_shared/components/issue/issue_milestone_spec.js
• spec/frontend/vue_shared/components/issue/related_issuable_item_spec.js
• spec/frontend/vue_shared/components/markdown/header_spec.js
• spec/frontend/vue_shared/components/markdown/suggestion_diff_header_spec.js
• spec/frontend/vue_shared/components/modal_copy_button_spec.js

Conformity

• Merge request performance guidelines
• Style guides

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Closes: #196763 (closed)