PIM-3288: fix memory leak on product import

| Q                    | A
| -------------------- | ---
| Bug fix?             | Y
| New feature?         | N
| BC breaks?           | N
| CI currently passes? | N
| Tests pass?          | Y
| Scenarios pass?      | Y
| Checkstyle issues?*  | N
| PMD issues?**        | N
| Changelog updated?   | Y
| Fixed tickets        | PIM-3288
| Doc PR               |
looks like we never use the addProduct method, should we remove it from CategoryInterface or at least mark it as deprecated ?