Remove legacy unprocessed foundational_skills folder

The foundational_skills folder is no longer processed evidenced by the taxonomy folders var at https://github.com/instructlab/schema/blob/82f2d790a7854858a9d112c0840b532617e44116/src/instructlab/schema/taxonomy.py#L30. Therefore: we should remove this folder in the community taxonomy to provide clarity to users where to place skill content.

Signed-off-by: Tyler Lisowski <[email protected]>

Author: relyt0925