First round of dead file removal

experimental/visual_studio_plugin/src/MsAd7.BaseImpl/ExpressionContext.cs

-using System;
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.Linq;
-using System.Text;
-using Microsoft.VisualStudio.Debugger.Interop;
-
-namespace Google.MsAd7.BaseImpl
-{
-  public class ExpressionContext : IDebugExpressionContext2
-  {
-    #region Implementation of IDebugExpressionContext2
-
-    public int GetName(out string pbstrName) {
-      Debug.WriteLine("ExpressionContext.GetName");
-      throw new NotImplementedException();
-    }
-
-    public int ParseText(string pszCode, enum_PARSEFLAGS dwFlags, uint nRadix, out IDebugExpression2 ppExpr, out string pbstrError, out uint pichError) {
-      Debug.WriteLine("ExpressionContext.ParseText");
-      throw new NotImplementedException();
-    }
-
-    #endregion
-  }
-}