Fix #3450: Fix "Clear assembly list" not actually persistent.

Author: siegfriedpammer

ICSharpCode.ILSpyX/AssemblyList.cs

@@ -405,7 +405,6 @@ public void Clear()
 			VerifyAccess();
 			lock (lockObj)
 			{
-				dirty = true;
 				assemblies.Clear();
 				byFilename.Clear();
 			}