Merge pull request #40849 from jaredpar/nullable-doc

Documentation Update

docs/compilers/CSharp/Nullability Public API Design Notes.md

@@ -95,8 +95,7 @@ We add the new APIs for retreiving and interacting with nullability:
 ```C#
 public enum NullableAnnotation : byte
 {
-    NotApplicable,
-    Disabled,
+    None,
     NotAnnotated,
     Annotated
 }