tech(1d): use only usefull assessment attributes and clean model

1d/app/models/activity.js

@@ -1,6 +1,5 @@
-import Model, { attr, belongsTo } from '@ember-data/model';
+import Model, { attr } from '@ember-data/model';
 
 export default class Activity extends Model {
   @attr('string') level;
-  @belongsTo('assessment', { async: true, inverse: 'activities' }) assessment;
 }

1d/app/pods/assessment/model.js

@@ -1,17 +1,7 @@
-import Model, { attr, hasMany } from '@ember-data/model';
+import Model, { attr } from '@ember-data/model';
 
 export default class Assessment extends Model {
-  // attributes
-  @attr('string') certificationNumber;
-  @attr('string') codeCampaign;
   @attr('string') state;
-  @attr('string') title;
-  @attr('string') type;
-  @attr('string') lastQuestionState;
-  @attr('string') method;
-
-  // references
-  @attr('string') competenceId;
   @attr('string') missionId;
-  @hasMany('activity', { async: true, inverse: 'assessment' }) activities;
+  @attr('string') organizationLearnerId;
 }