Although a non-breaking error with apparently no consequences, it should be reported that deleting Flickr fields defined on a node type, necessary to uninstall the submodule, results in:
Notice: Undefined index: entity keys in entity_create_stub_entity() (line 7728 of /home/martin/www/drupal-7/includes/common.inc).
"The requested page "/admin/structure/types/manage/page/fields/field_flickr_photo_set/delete" could not be found."
After that the module list under 'Flickr Fields' says "Required by: Drupal (Fields pending deletion)". So the checkbow remains greyed out and the module can only ne disabled in the DB table 'system', column 'status'.