Remove reference to Windows XP as a baseline in X509Chain (#11026)

Author: vcsjones

xml/System.Security.Cryptography.X509Certificates/X509Chain.xml

@@ -457,7 +457,7 @@
 ## Remarks  
  Each <xref:System.Security.Cryptography.X509Certificates.X509ChainElement> object is a representation of an element in the chain that was built during a call to the <xref:System.Security.Cryptography.X509Certificates.X509Chain.Build%2A> method.  
   
- A chain element consists of an <xref:System.Security.Cryptography.X509Certificates.X509Certificate2> object, an <xref:System.Security.Cryptography.X509Certificates.X509ChainStatus> structure, and an extra information string (available only on Windows XP platforms).  
+ A chain element consists of an <xref:System.Security.Cryptography.X509Certificates.X509Certificate2> object, an <xref:System.Security.Cryptography.X509Certificates.X509ChainStatus> structure, and an extra information string.