Fix i18n in room-join component

src/app/components/shared/room-join/room-join.component.html

@@ -2,7 +2,7 @@
 <form (ngSubmit)="joinRoom(roomId.value)">
   <div fxLayout="row" fxLayoutAlign="center" fxLayoutGap="10px">
     <mat-form-field class="number">
-      <input matInput #roomId placeholder="Join Session!" [formControl]="roomFormControl"
+      <input matInput #roomId placeholder="Session-Id" [formControl]="roomFormControl"
              [errorStateMatcher]="matcher" maxlength="8"/>
       <mat-hint align="end">{{roomId.value.length}} / 8</mat-hint>
       <mat-error *ngIf="roomFormControl.hasError('required')">{{ 'home-page.please-enter' | translate}}</mat-error>

src/assets/i18n/participant/de.json

 {
   "home-page": {
-    "join-demo-session": "Demo-Session betreten",
-    "session-id": "Session-Id",
     "no-room-found": "Es wurde keine Session mit dieser ID gefunden.",
     "please-enter": "Bitte geben Sie eine Session-ID ein.",
     "exactly-8": "Eine Session-ID hat genau 8 Ziffern."

src/assets/i18n/participant/en.json

 {
   "home-page": {
-    "join-demo-session": "Join demo-session",
-    "session-id": "Session-Id",
     "no-room-found": "No session was found with this id.",
     "please-enter": "Please enter a session-id.",
     "exactly-8": "A session-id has exactly 8 digits."