Remove old `data_files/` directory

[SteveDMurphy]

Bug Description

The history of the data_files/ directory suggests that it is quite outdated and could lead to confusion. These should likely be removed or at least re-generated if still required

Steps to Reproduce

n/a

Expected behavior

fideslang to be imported or viewed from the documentation website

Screenshots

n/a

Environment

• Version: 1.1.0
• OS: Darwin
• Python Version: 3.9.12
• Docker Version: 20.10.16

Additional context

Found as part of #62