Update CODEOWNERS (#12127)

Author: cston

.github/CODEOWNERS

@@ -19,9 +19,9 @@
 
 # Area owners of the dotnet/runtime repo: https://github.com/dotnet/runtime/blob/master/docs/area-owners.md
 
-/xml/Microsoft.CSharp*/ @cston @333fred
+/xml/Microsoft.CSharp*/ @333fred
 /xml/Microsoft.Extensions.Http*/ @dotnet/ncl
-/xml/Microsoft.VisualBasic*/ @cston @333fred
+/xml/Microsoft.VisualBasic*/ @333fred
 /xml/System.Activities*/ @dotnet/docs
 /xml/System.AddIn*/ @dotnet/docs
 /xml/System.ComponentModel.DataAnnotations*/ @ajcvickers
@@ -36,7 +36,7 @@
 /xml/System.IO.Pipelines*/ @halter73
 /xml/System.IdentityModel*/ @dotnet/docs
 /xml/System.Json*/ @dotnet/docs
-/xml/System.Linq.Expressions*/ @cston @333fred
+/xml/System.Linq.Expressions*/ @333fred
 /xml/System.Media*/ @dotnet/docs
 /xml/System.Messaging*/ @dotnet/docs
 /xml/System.Net*/ @dotnet/ncl