Remove resolved source-build runtime patch

src/SourceBuild/patches/runtime/0004-Fix-cast-type-to-conform-to-Roslyn-API.patch

@@ -1,23 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Matt Thalman <mthalman@microsoft.com>
-Date: Thu, 27 Apr 2023 09:51:08 -0500
-Subject: [PATCH] Fix cast type to conform to Roslyn API
-
-Backport: https://github.com/dotnet/runtime/pull/85466
----
- .../gen/ComInterfaceGenerator/InlinedTypes.cs                   | 2 +-
- 1 file changed, 1 insertion(+), 1 deletion(-)
-
-diff --git a/src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/InlinedTypes.cs b/src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/InlinedTypes.cs
-index cb55e36b32c..ef2fe4f6d65 100644
---- a/src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/InlinedTypes.cs
-+++ b/src/libraries/System.Runtime.InteropServices/gen/ComInterfaceGenerator/InlinedTypes.cs
-@@ -53,7 +53,7 @@ static BlockSyntax Body()
-                                         GenericName(
-                                             Identifier("GetInstance"),
-                                             TypeArgumentList(
--                                                SeparatedList<SyntaxNode>(
-+                                                SeparatedList<TypeSyntax>(
-                                                     new[] { PredefinedType(Token(SyntaxKind.ObjectKeyword)) })))))
-                                 .AddArgumentListArguments(
-                                     Argument(