docs: remove unused attribute (angular#41211)

Fixes angular#41210

PR Close angular#41211

Author: geromegrignon

aio/content/examples/toh-pt5/src/app/app.component.html

@@ -1,6 +1,6 @@
 <!-- #docplaster -->
 <!-- #docregion, heroes, outlet -->
-<h1 id="main-content-header">{{title}}</h1>
+<h1>{{title}}</h1>
 <!-- #enddocregion outlet -->
 <nav>
   <!-- #enddocregion heroes -->