Update documentation for method bool System.Type.IsAssignableTo(Type) (dotnet#5474)

Correction of documentation as stated in dotnet/runtime#50221.

Author: hamarb123

xml/System/Type.xml

@@ -11299,7 +11299,7 @@ GetType(Array).IsAssignableFrom(type)
 
 -   The current type represents a value type, and <paramref name="targetType" /> represents <c>Nullable&lt;c&gt;</c> (<c>Nullable(Of c)</c> in Visual Basic).  
 
- <see langword="false" /> if none of these conditions are true, or if <paramref name="targetType" /> or <see langword="this" /> is <see langword="null" />.</returns>
+ <see langword="false" /> if none of these conditions are true, or if <paramref name="targetType" /> is <see langword="null" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>