While reviewing MDL-83873, Amaia created a separate commit for the final deprecation of some methods that were deprecated a long time ago: https://github.com/aanabit/moodle/commit/fc685756248e17f5bfc1f5f37da0afc83f73ecb7 

However, the patch was incomplete and, as it was unrelated to the original issue, we decided to create a separate issue for dealing with this, and cleaning up the calendar code

Some of the points that were raised while reviewing this commit:

• calendar_top_controls, calendar_get_link_previous and calendar_get_link_next will be deprecated in MDL-79434.
• Move calendar_add_event_metadata to deprecatedlib.php
• The following also needs to be deprecated:
  • calendar_get_courselink
  • strings: siteevent, courseevent, groupevent, userevent
  • CSS: calendar_event_site,calendar_event_course,calendar_event_group,calendar_event_user --> They can't be deprecated because behat confirmed they are still in use
  • calendar_events_by_day (deprecated in 3.4)
  • event in calendar/renderer.php
  • Line 1183 --> #[\core\attribute\deprecated('set_sources', since: '3.4', mdl: 'MDL-59890', final: true)] --> #[\core\attribute\deprecated('\\{*}prepare_for_view\\{*}', since: '3.4', mdl: 'MDL-59890', final: true)]