Fix broken samples links for String.Format and DateTime.Parse (#4243)

* link to published samples

Author: gewarren

xml/System/DateTime.xml

@@ -5121,7 +5121,7 @@ Numerous examples that call the `DateTime.Parse` method are interspersed through
 
 [!INCLUDE[interactive-note](~/includes/csharp-interactive-with-utc-note.md)]
 
-You can also download a complete set of `DateTime.Parse` examples, which are included in a [.NET Core 2.0 project for C#](https://github.com/dotnet/samples/raw/master/snippets/csharp/downloads/api/System/DateTime.Parse.zip) and a [.NET Core 2.0 project for Visual Basic](https://github.com/dotnet/samples/raw/master/snippets/visualbasic/downloads/api/System/DateTime.Parse.zip), from the [dotnet/samples GitHub repository](https://github.com/dotnet/samples).
+You can also download a complete set of `DateTime.Parse` examples, which are included in a [.NET Core project for C#](https://docs.microsoft.com/samples/dotnet/samples/datetime-parse/).
 
  ]]></format>
         </remarks>

xml/System/String.xml

@@ -5538,7 +5538,7 @@ In contrast, the use of interpolated strings in the following example produce mu
 
 Numerous examples that call the <xref:System.String.Format%2A> method are interspersed through the [Remarks](#remarks-top) section of this article.
 
-You can also download a complete set of `String.Format` examples, which are included a [.NET Core 2.0 project for C#](https://github.com/dotnet/samples/raw/master/snippets/csharp/downloads/api/System/String.Format.zip) and a [.NET Core 2.0 project for Visual Basic](https://github.com/dotnet/samples/raw/master/snippets/visualbasic/downloads/api/System/String.Format.zip), from the [dotnet/samples GitHub repository](https://github.com/dotnet/samples).
+You can also download a complete set of `String.Format` examples, which are included a [.NET Core project for C#](https://docs.microsoft.com/samples/dotnet/samples/string-format/).
 
 The following are some of the examples included in the article: