swh.core.config: Drop support for ini configuration file

This is no longer used [1]

This also adds some types on impacted changed functions.

• [1] Historically, we started using .ini file as configuration file for swh. We moved to yaml a while ago. Only one last instance of it is currently getting rid of in swh/infra/puppet/puppet-swh-site!226 (closed).

Related to #1532 (closed) Related to swh/infra/puppet/puppet-swh-site!226 (closed)

Test Plan

tox

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Migrated from D3964 (view on Phabricator)