TextField: Fix missing label

The default value of the child class overrides the value set by the 
parent constructor.

projects/common/models/elements/input-elements/text-field.ts

@@ -14,7 +14,6 @@ import { InstantiationEror } from 'common/errors';
 
 export class TextFieldElement extends TextInputElement implements TextFieldProperties {
   type: UIElementType = 'text-field';
-  label: string = '';
   appearance?: 'fill' | 'outline' = 'outline';
   minLength: number | null = null;
   minLengthWarnMessage: string = 'Eingabe zu kurz';