Cleanup widget

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What does this MR do and why?

Address vue/no-unused-properties violations in app/assets/javascripts/vue_merge_request_widget/

This MR contains a cleanup of unused props and methods for the files denoted below.

• app/assets/javascripts/vue_merge_request_widget/components/widget/action_buttons.vue
• app/assets/javascripts/vue_merge_request_widget/mr_widget_options.vue
• app/assets/javascripts/vue_merge_request_widget/widgets/accessibility/index.vue
• app/assets/javascripts/vue_merge_request_widget/widgets/code_quality/index.vue