Remove pipfile-requirements manager from .thoth.yaml

[shreekarSS]

Describe the bug

The pipfile-requirements manager can be removed because requirements.txt isn’t being utilized for packaging or deployment. Only the Pipfile.lock is needed for deployment info.
Else Kebechet's Update manager will not work on this aicoe-osc-demo repo

To Reproduce
Steps to reproduce the behavior:

1. Create an issue with title 'Kebechet update'
2. Kebechet's pipfile-requirements manager will fail with creating new issue like No pinned version for src shreekarSS/aicoe-osc-demo#2

Expected behavior
Once Update manager runs successfully, it will raise a PR like shreekarSS#3

[codificat]

Actually, the pipfile-requirements manager failure like shreekarSS#2 might be a bug in Kebechet, as I believe that the mentioned Pipfile entry could be translated to a requirements.txt entry.

Nevertherless, it's probably a good idea to remove that manager from this repo's configuration, as you say, because there is no requirements.txt here and it doesn't seem to be needed.