docs: removes the outdated content (#39242)

Remove the statements where mentions the component in the `entryComponents`
array inside `NgModule` metadata.

This is not required since Angular version 9.

PR Close #39242

aio/content/guide/elements.md

@@ -134,7 +134,7 @@ ng add @angular/elements --project=*your_project_name*
 
 ## Example: A Popup Service
 
-Previously, when you wanted to add a component to an app at runtime, you had to define a _dynamic component_. The app module would have to list your dynamic component under `entryComponents`, so that the app wouldn't expect it to be present at startup, and then you would have to load it, attach it to an element in the DOM, and wire up all of the dependencies, change detection, and event handling, as described in [Dynamic Component Loader](guide/dynamic-component-loader).
+Previously, when you wanted to add a component to an app at runtime, you had to define a _dynamic component_, and then you would have to load it, attach it to an element in the DOM, and wire up all of the dependencies, change detection, and event handling, as described in [Dynamic Component Loader](guide/dynamic-component-loader).
 
 Using an Angular custom element makes the process much simpler and more transparent, by providing all of the infrastructure and framework automatically—all you have to do is define the kind of event handling you want. (You do still have to exclude the component from compilation, if you are not going to use it in your app.)