fix: change SCThingMeta getInstance() return value

src/core/things/Diff.ts

@@ -64,11 +64,6 @@ export interface SCDiff extends SCDiffWithoutReferences {
  * Meta information about a diff
  */
 export class SCDiffMeta extends SCThingMeta implements SCMetaTranslations<SCDiff> {
-  /**
-   * Set type definiton for singleton instance
-   */
-  protected static _instance: SCThingMeta;
-
   /**
    * Translations of fields
    */