Revert "Add support for C# 11 parameter null checks"

This reverts commit 9e462b53ad.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/YieldReturn.cs

@@ -1,4 +1,4 @@
-// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
+// Copyright (c) AlphaSierraPapa for the SharpDevelop Team
 // 
 // Permission is hereby granted, free of charge, to any person obtaining a copy of this
 // software and associated documentation files (the "Software"), to deal in the Software
@@ -427,13 +427,6 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Console.WriteLine("normal exit");
 		}
 
-#if CS110 && false
-		public IEnumerable<object> YieldBangBang(object x!!)
-		{
-			yield return x;
-		}
-#endif
-
 		internal IEnumerable<int> ForLoopWithYieldReturn(int end, int evil)
 		{
 			// This loop needs to pick the implicit "yield break;" as exit point

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -1825,14 +1825,6 @@ namespace ICSharpCode.Decompiler.CSharp
 				RemoveAttribute(entityDecl, KnownAttribute.AsyncStateMachine);
 				RemoveAttribute(entityDecl, KnownAttribute.DebuggerStepThrough);
 			}
-			foreach (var parameter in entityDecl.GetChildrenByRole(Roles.Parameter))
-			{
-				var variable = parameter.Annotation<ILVariableResolveResult>()?.Variable;
-				if (variable != null && variable.HasNullCheck)
-				{
-					parameter.HasNullCheck = true;
-				}
-			}
 		}
 
 		internal static bool RemoveAttribute(EntityDeclaration entityDecl, KnownAttribute attributeType)

ICSharpCode.Decompiler/CSharp/OutputVisitor/CSharpOutputVisitor.cs

@@ -2647,10 +2647,6 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 			{
 				WriteIdentifier(parameterDeclaration.NameToken);
 			}
-			if (parameterDeclaration.HasNullCheck)
-			{
-				WriteToken(Roles.DoubleExclamation);
-			}
 			if (!parameterDeclaration.DefaultExpression.IsNull)
 			{
 				Space(policy.SpaceAroundAssignment);

ICSharpCode.Decompiler/CSharp/Syntax/Roles.cs

@@ -68,7 +68,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 		public static readonly TokenRole Colon = new TokenRole(":");
 		public static readonly TokenRole DoubleColon = new TokenRole("::");
 		public static readonly TokenRole Arrow = new TokenRole("=>");
-		public static readonly TokenRole DoubleExclamation = new TokenRole("!!");
 		public static readonly Role<Comment> Comment = new Role<Comment>("Comment", null);
 		public static readonly Role<PreProcessorDirective> PreProcessorDirective = new Role<PreProcessorDirective>("PreProcessorDirective", null);
 

ICSharpCode.Decompiler/CSharp/Syntax/TypeMembers/ParameterDeclaration.cs

@@ -164,26 +164,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			}
 		}
 
-		bool hasNullCheck;
-
-		public CSharpTokenNode DoubleExclamationToken {
-			get {
-				if (hasNullCheck)
-				{
-					return GetChildByRole(Roles.DoubleExclamation);
-				}
-				return CSharpTokenNode.Null;
-			}
-		}
-
-		public bool HasNullCheck {
-			get { return hasNullCheck; }
-			set {
-				ThrowIfFrozen();
-				hasNullCheck = value;
-			}
-		}
-
 		public CSharpTokenNode AssignToken {
 			get { return GetChildByRole(Roles.Assign); }
 		}
@@ -213,7 +193,6 @@ namespace ICSharpCode.Decompiler.CSharp.Syntax
 			var o = other as ParameterDeclaration;
 			return o != null && this.Attributes.DoMatch(o.Attributes, match) && this.ParameterModifier == o.ParameterModifier
 				&& this.Type.DoMatch(o.Type, match) && MatchString(this.Name, o.Name)
-				&& this.HasNullCheck == o.HasNullCheck
 				&& this.DefaultExpression.DoMatch(o.DefaultExpression, match);
 		}
 

ICSharpCode.Decompiler/IL/ILVariable.cs

@@ -438,21 +438,6 @@ namespace ICSharpCode.Decompiler.IL
 		/// </summary>
 		internal bool RemoveIfRedundant;
 
-		private bool hasNullCheck;
-
-		/// <summary>
-		/// Gets/sets whether a parameter has an auto-generated null check, i.e., the !! modifier.
-		/// Returns false for all variables except parameters.
-		/// </summary>
-		public bool HasNullCheck {
-			get => hasNullCheck;
-			set {
-				if (Kind != VariableKind.Parameter && value)
-					throw new InvalidOperationException("Cannot set HasNullCheck on local variables!");
-				hasNullCheck = value;
-			}
-		}
-
 		public ILVariable(VariableKind kind, IType type, int? index = null)
 		{
 			if (type == null)