Replace .NET Framework 4.5.2 tokens (#12535)

* Replace .NET Framework 4.5.2 tokens

* Remove net-v452-md.md

Author: nxtn

docs/framework/migration-guide/mitigation-xml-schema-validation.md

@@ -19,14 +19,14 @@ In the .NET Framework 4.6, XSD schema validation detects a violation of the uniq
 
 - Starting with the apps that target the .NET Framework 4.6, detection of the schema validation error is enabled by default; however, it is possible to opt out of it, so that the schema validation error will not be detected.  
 
-- In apps that run under the .NET Framework 4.6 but target the [!INCLUDE[net_v452](../../../includes/net-v452-md.md)] and earlier versions, a schema validation error is not detected by default; however, it is possible to opt into it, so that the schema validation error will be detected.  
+- In apps that run under the .NET Framework 4.6 but target the .NET Framework 4.5.2 and earlier versions, a schema validation error is not detected by default; however, it is possible to opt into it, so that the schema validation error will be detected.  
 
  This behavior can be configured by using the <xref:System.AppContext> class to define the value of the `System.Xml.IgnoreEmptyKeySequences` switch. Because the switch's default value is `false` (empty key sequences are not ignored), apps that target the .NET Framework 4.6 can opt out of the behavior by using the following code to set the switch's value to `true`:  
 
  [!code-csharp[AppCompat.IgnoreEmptyKeySequences#1](../../../samples/snippets/csharp/VS_Snippets_CLR/appcompat.ignoreemptykeysequences/cs/program.cs#1)]
  [!code-vb[AppCompat.IgnoreEmptyKeySequences#1](../../../samples/snippets/visualbasic/VS_Snippets_CLR/appcompat.ignoreemptykeysequences/vb/module1.vb#1)]  
 
- For apps that target the [!INCLUDE[net_v452](../../../includes/net-v452-md.md)] and earlier versions, because the switch's default value is `true` (empty key sequences are ignored), it is possible to ensure that a compound key with an empty key does generate a schema validation error by using the following code to set the switch's value to `false`.  
+ For apps that target the .NET Framework 4.5.2 and earlier versions, because the switch's default value is `true` (empty key sequences are ignored), it is possible to ensure that a compound key with an empty key does generate a schema validation error by using the following code to set the switch's value to `false`.  
 
  [!code-csharp[AppCompat.IgnoreEmptyKeySequences#2](../../../samples/snippets/csharp/VS_Snippets_CLR/appcompat.ignoreemptykeysequences/cs/program.cs#2)]
  [!code-vb[AppCompat.IgnoreEmptyKeySequences#2](../../../samples/snippets/visualbasic/VS_Snippets_CLR/appcompat.ignoreemptykeysequences/vb/module1.vb#2)]