[4.2] Fix delete category custom fields value

[joomdonation]

Pull Request for Issue #38379.

Summary of Changes

Currently, delete a category does not delete custom fields value associated with that category. This PR just fixes that wrong behavior. See #38379 for detailed issue description.

Testing Instructions

1. Go to Content -> Fields, create a custom field for category
2. Go to Content -> Categories, edit a category, look at Fields tab, enter data for the custom field which you created above
3. Access to your site database (via phpmyadmin for example), look at #__fields_values table, you should see a record contains data for custom field which you entered for category above
4. Trash the category, then delete the category from the system

Actual result BEFORE applying this Pull Request

The record which store custom fields data for category is not deleted from #__fields_values table

Expected result AFTER applying this Pull Request

The record which store custom fields data for category is deleted from #__fields_values table

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[alikon]

I have tested this item ✅ successfully on 3d72b40

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[viocassel]

I have tested this item ✅ successfully on 3d72b40

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39477.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39477.}

[wilsonge]

Thanks!