Change HashSetExtensions2 to HashSetExtensions

Author: cschuchardt88

src/Neo/Extensions/HashSetExtensions.cs

@@ -18,7 +18,7 @@ namespace Neo.Extensions
     /// <summary>
     /// A helper class that provides common functions.
     /// </summary>
-    public static class HashSetExtensions2
+    public static class HashSetExtensions
     {
         internal static void Remove<T>(this HashSet<T> set, HashSetCache<T> other)
             where T : IEquatable<T>

tests/Neo.Cryptography.MPTTrie.Tests/Cryptography/MPTTrie/UT_Trie.cs

@@ -17,7 +17,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
-using static Neo.Extensions.HashSetExtensions;
 
 namespace Neo.Cryptography.MPTTrie.Tests
 {

tests/Neo.Network.RPC.Tests/UT_Nep17API.cs

@@ -20,7 +20,6 @@
 using System.Linq;
 using System.Numerics;
 using System.Threading.Tasks;
-using static Neo.Extensions.HashSetExtensions;
 
 namespace Neo.Network.RPC.Tests
 {