Remove mock storages used in tests.

Impacts:

• swh-indexer
• swh-deposit
• swh-journal
• swh-loader-git
• swh-loader-mercurial
• swh-loader-core (named LoaderNoStorage)
• swh-loader-pypi
• swh-loader-svn
• swh-web

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Migrated from T1307 (view on Phabricator)