Drupal remove deleted fields from database
Install and enable Field SQL norevisions, and use it to delete any revisions you don't need. Also set it to disable revisions for content/entity types that you don't want revisions being made.
Note: For entity content types, drupal will automatically make revisions for each update, but won't allow you to revert to any of these revisions, so this is pretty pointless; plus for very large databases this can degrade performance.