Problem/Motivation
#2926540: Split revision-handling methods to a separate entity storage interface introduced a specialized interface for revisionable storage handlers and duplicated the loadRevision() and deleteRevision() methods from EntityStorageInterface because those methods could not be deprecated during the 8.x.x cycle (see #2927251: [policy, no patch] Decide how to deal with methods needing to be moved down an interface hierarchy).
Proposed resolution
Remove those two methods in the last minor version of Drupal 8.
Remaining tasks
Wait for the 9.0.x branch to be created :)
User interface changes
Nope.
API changes
Revision-related methods will no longer be part of the generic EntityStorageInterface.
Data model changes
Nope.