Mario Peshev

Delete all Custom Field entries assigned to posts that do not exist in the posts table.
Navigate to Settings -> Remove Unused CFs and delete all postmeta for non-existing posts.

DX Remove Unused Custom Fields

Does exactly what it says.
Installed, navigate to the settings page, click "Delete" and Done! Cannot be easier than that.
Thank you!



Simply Awesome!

Delete the Custom Fields from your postmeta table where assigned posts no longer exist.

netbiel

This plugin ads some extra options to your Customizer (like social icons), registers taxonomies and custom posts types for: 
– Portfolio items 
– Testimonials 
– FAQ 
– Team Members
This plugin doesn’t change how new post types are displayed in your theme. e.g You’ll need to add templates for archive-portfolio.php and single-portfolio.php if you want to customize the display of portfolio items. 
In the theme integrated with smartlib library you don’t need do anything

Smartlib Tools

Useful post types and customizer options.

DX Remove Unused Custom Fields vs Smartlib Tools