Update existing-database.md (#3713)

Remove outdate video references. Fixes #3684.

Author: JeremyLikness

entity-framework/ef6/modeling/code-first/migrations/existing-database.md

@@ -14,18 +14,6 @@ This article covers using Code First Migrations with an existing database, one t
 > [!NOTE]
 > This article assumes you know how to use Code First Migrations in basic scenarios. If you don’t, then you’ll need to read [Code First Migrations](xref:ef6/modeling/code-first/migrations/index) before continuing.
 
-## Screencasts
-
-If you'd rather watch a screencast than read this article, the following two videos cover the same content as this article.
-
-### Video One: "Migrations - Under the Hood"
-
-[This screencast](https://channel9.msdn.com/blogs/ef/migrations-under-the-hood) covers how migrations tracks and uses information about the model to detect model changes.
-
-### Video Two: "Migrations - Existing Databases"
-
-Building on the concepts from the previous video, [this screencast](https://channel9.msdn.com/blogs/ef/migrations-existing-databases) covers how to enable and use migrations with an existing database.
-
 ## Step 1: Create a model
 
 Your first step will be to create a Code First model that targets your existing database. The [Code First to an Existing Database](xref:ef6/modeling/code-first/workflows/existing-database) topic provides detailed guidance on how to do this.