Fix #10422 - Included support for _override_sugarfield on delete vardef

[serhiisamko091184]

Description

If you delete the custom variable, the file (custom/Extension/modules//Ext/Vardefs/<YourFieldName_c>.php) won't be deleted.

Motivation and Context

How To Test This

1. Create a custom variable via Studio.
2. Delete the variable:
   
3. Check the custom folder (mentioned above) to make sure the file is still there.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Final checklist

• My code follows the code style of this project found here.
• My change requires a change to the documentation.
• I have read the How to Contribute guidelines.