Revert "Restore 'offset' and 'negative_utc' arguments and make them optional"
This reverts commit a0f54362 (ie. the second half of !313 (closed), that was added after review).
This means this commit removes the 'offset' and 'negative_utc' arguments.
It also removes the 'negative_utc' attribute (which is not used anymore), but keeps an 'offset' property, which is an alias to 'offset_minutes()'. This is only to keep this commit readable; the next commit will remove this alias.
This also affects the journal, as these fields are removed from .to_dict()
-> swh-docs!297 (closed)
Migrated from D7011 (view on Phabricator)