[Housekeeping] Remove deprecated ModalConfig title

[MadsBuchmann]

Describe the housekeeping request

In #1141 which was merged in October 2020 the title field of the ModalConfig (libs/designsystem/src/lib/components/modal/modal-wrapper/config/modal-config.ts) interface was deprecated.

We should fully remove the field. Potentially as part of v6?

However it seems that the ModalWrapperComponent still relies on config.title to display the title for the Modal:

// libs/designsystem/src/lib/components/modal/modal-wrapper/modal-wrapper.component.html      
<ion-header (touchstart)="onHeaderTouchStart($event)">
  <ion-toolbar>
    <ion-title>{{ config.title }}</ion-title>  // <------ Interesting part
    <ion-buttons slot="start" *ngIf="config.flavor === 'drawer'">
      <ng-container *ngTemplateOutlet="closeButton; context: { icon: 'arrow-down' }"></ng-container>
    </ion-buttons>
    <ion-buttons slot="end" *ngIf="config.flavor === 'modal'">
      <ng-container *ngTemplateOutlet="closeButton; context: { icon: 'close' }"></ng-container>
    </ion-buttons>
    <ion-buttons slot="end" *ngIf="config.flavor === 'drawer' && config.drawerSupplementaryAction">
      <ng-container
        *ngTemplateOutlet="supplementaryButton; context: { btn: config.drawerSupplementaryAction }"
      ></ng-container>
    </ion-buttons>
  </ion-toolbar>
</ion-header>
[...]

We need to solve that somehow before fully removing it.

This issue blocks #843

The solution that should be made in #843 can not rely on the title being passed by config.title. Therefore this issue has to be solved before #843 can be solved.