docs: removed the obsolete Tag and updated the files (#27237)

(cherry picked from commit aa81267)

Author: alkavats1

src/components-examples/material/tabs/tab-group-preserve-content/tab-group-preserve-content-example.html

@@ -6,7 +6,7 @@
       width="560"
       height="315"
       src="https://www.youtube.com/embed/B-lipaiZII8"
-      frameborder="0"
+      style="border: 0"
       allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"
       allowfullscreen></iframe>
   </mat-tab>

src/dev-app/dialog/dialog-demo.ts

@@ -240,7 +240,7 @@ export class ContentElementDialog {
     <h2 mat-dialog-title>Neptune</h2>
 
     <mat-dialog-content>
-      <iframe frameborder="0" src="https://en.wikipedia.org/wiki/Neptune"></iframe>
+      <iframe style="border: 0" src="https://en.wikipedia.org/wiki/Neptune"></iframe>
     </mat-dialog-content>
 
     <mat-dialog-actions>

src/dev-app/legacy-dialog/legacy-dialog-demo.ts

@@ -232,7 +232,7 @@ export class LegacyContentElementDialog {
     <h2 mat-dialog-title>Neptune</h2>
 
     <mat-dialog-content>
-      <iframe frameborder="0" src="https://en.wikipedia.org/wiki/Neptune"></iframe>
+      <iframe style="border: 0" src="https://en.wikipedia.org/wiki/Neptune"></iframe>
     </mat-dialog-content>
 
     <mat-dialog-actions>