Simplify nodes

src/Syntax/Parsing/Parser.cs

@@ -2,9 +2,7 @@
 using System.Diagnostics.CodeAnalysis;
 using Common;
 using Syntax.Diagnostics;
-using Syntax.Parsing.Definitions;
-using Syntax.Parsing.Expressions;
-using Syntax.Parsing.Statements;
+using Syntax.Parsing.Node;
 using Syntax.Tokenization;
 using Syntax.Typing;