MySQL: NOT LIKE
categories_posts and categories_news start with substring 'categories_' then it is enough to check that developer_configurations_cms.cfg_name_unique starts with 'categories' instead of check if it contains the given substring. Translating all that into a query:
SELECT * FROM developer_configurations_cms WHERE developer_configurations_cms.cat_id = '1' AND developer_configurations_cms.cfg_variables LIKE '%parent_id=2%' AND developer_configurations_cms.cfg_name_unique NOT LIKE 'categories%'
I don't know why
cfg_name_unique NOT LIKE '%categories%' still returns those two values, but maybe exclude them explicit:
SELECT * FROM developer_configurations_cms WHERE developer_configurations_cms.cat_id = '1' AND developer_configurations_cms.cfg_variables LIKE '%parent_id=2%' AND developer_configurations_cms.cfg_name_unique NOT LIKE '%categories%' AND developer_configurations_cms.cfg_name_unique NOT IN ('categories_posts', 'categories_news')