deposit: Clean up no longer used deposit config

For the next release (soon):

• tool is configured alone by the server
• provider is really about the deposit client information which the deposit server can fill by itself already

Related to T2649

Test Plan

bin/octocatalog

  File[/etc/softwareheritage/deposit/server.yml] =>
   parameters =>
     content =>
      @@ -1,12 +1,4 @@
       ---
       max_upload_size: 209715200
      -tool:
      -  name: swh-deposit
      -  version: 0.0.1
      -  configuration:
      -    sword_version: 2
      -provider:
      -  provider_type: deposit_client
      -  metadata: {}
       scheduler:
         cls: remote

---

Migrated from D4117 (view on Phabricator)