Fixes: 1) Remove unused imports from `core/admin.py`;
Extra: 1) Delete redundant `autocomplete_filter.html` template and associated filter classes for cleanup; 2) Minor refactoring of `ProductAdmin` class in alignment with the removal of filters.
Fixes: 1) Correct `parameter_name` assignments in BrandAdminFilter, CategoryAdminFilter, TagsAdminFilter, and VendorAdminFilter to use plain strings;
Extra: None;
Fixes: 1) Correct parameter name value extraction to use `current` in `BaseAutocompleteFilter`;
Extra: 1) Refactor HTML rendering in `BaseAutocompleteFilter` for readability; 2) Add comments to explain purposes in the new template.
