Figure out how to handle dependencies

[rpitonak]

We were using bot to keep our dependencies updated, but currently, it is disabled because of https://github.com/thoth-station/kebechet/issues/189. So we have two options:

• Wait until bot issue is fixed and make bot manage our dependencies again.
• Remove https://github.com/user-cont/conu/blob/master/requirements.txt and rename requirements.in into requirements.txt. Also we should change https://github.com/user-cont/conu/blob/master/CONTRIBUTING.md as it mention bot workflow.

[rpitonak]

Currently fixed by https://github.com/user-cont/conu/pull/345.