File "tuf/client_setup_and_repository_example.md" is extermely outdated

[Silvanoc]

Description of issue or feature request:

The file tuf/client_setup_and_repository_example.md is extermely outdated.

It refers to the file basic_client.py, but that file was moved from tuf/client to tuf/scripts on commit e175508 (2016).

It was later renamed to tuf/scripts/client.py on commit d7bb67b (2018).

Current behavior:

File file tuf/client_setup_and_repository_example.md is outdated.

Expected behavior:

File tuf/client_setup_and_repository_example.md gets updated or removed.

[lukpueh]

Many thanks for submitting the issue, @Silvanoc! FYI, we have an extensive list of documentation issues in #808. But removing tuf/client_setup_and_repository_example.md seems like a sensible partial fix (see #1001).