Remove `fre/pp/checkout` and associated files/doc

[singhd789]

Is your feature request related to a problem? Please describe.
fre pp checkout functionality is being moved ad updated to fre workflow checkout

Describe the solution you'd like
Remove:

• fre/pp/checkout_script
• any checkout reference in fre/tests/test_fre_pp_cli.py
• any fre/pp/checkout reference in docs (fre/pp/README.md, docs/tools/pp.rst, docs/usage/guides/fre_pp_guide.rst