C#: Address review comments.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyManager.cs

@@ -143,7 +143,7 @@ public DependencyManager(string srcDir, IDependencyOptions options, ILogger logg
                 DateTime.Now - startTime);
         }
 
-        public DependencyManager(string srcDir) : this(srcDir, DependencyOptionsFactory.Default, new ConsoleLogger(Verbosity.Info)) { }
+        public DependencyManager(string srcDir) : this(srcDir, DependencyOptions.Default, new ConsoleLogger(Verbosity.Info)) { }
 
         private IEnumerable<string> GetFiles(string pattern, bool recurseSubdirectories = true)
         {

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DependencyOptions.cs

@@ -53,6 +53,10 @@ public interface IDependencyOptions
 
     public class DependencyOptions : IDependencyOptions
     {
+        private static readonly DependencyOptions instance = new DependencyOptions();
+
+        public static IDependencyOptions Default => instance;
+
         public IList<string> DllDirs { get; set; } = new List<string>();
 
         public IList<string> Excludes { get; set; } = new List<string>();
@@ -70,11 +74,4 @@ public class DependencyOptions : IDependencyOptions
         public bool ExcludesFile(string path) =>
             Excludes.Any(path.Contains);
     }
-
-    public class DependencyOptionsFactory
-    {
-        private static readonly DependencyOptions instance = new DependencyOptions();
-
-        public static IDependencyOptions Default => instance;
-    }
-}
+}