[cleanup] Remove _get_baserevid and deprecated preloaditempages methods
[cleanup] Remove _get_baserevid and deprecated preloaditempages methods

The usage of baserevid is deprecated for 6 years.
preloaditempages() is deprecated for 4 years.

- replace _get_baserevid calls with claim.on_item.latest_revision_id
- use remove_last_args decorator to ignore baserevid parameter for
  several methods
- use latest_revision_id of the only item in claims
- update typing and doc

Change-Id: I67736237d60c95d0db54556359836b8b43f42b74

wikimedia/pywikibot-core,wikimedia/pywikibot-core