don't double load movie files when pre-loading, remove unused HawkFile parameter

src/BizHawk.Client.Common/movie/bk2/Bk2Movie.IO.cs

@@ -48,17 +48,7 @@ namespace BizHawk.Client.Common
 			return true;
 		}
 
-		public bool PreLoadHeaderAndLength(HawkFile hawkFile)
-		{
-			var file = new FileInfo(Filename);
-			if (!file.Exists)
-			{
-				return false;
-			}
-
-			Filename = file.FullName;
-			return Load(true);
-		}
+		public bool PreLoadHeaderAndLength() => Load(true);
 
 		protected virtual void Write(string fn, bool isBackup = false)
 		{

src/BizHawk.Client.Common/movie/interfaces/IMovie.cs

@@ -1,7 +1,5 @@
 using System.Collections.Generic;
 using System.IO;
-
-using BizHawk.Common;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -98,7 +96,7 @@ namespace BizHawk.Client.Common
 		/// Loads from the HawkFile the minimal amount of information needed to determine Header info and Movie length
 		/// This method is intended to be more performant than a full load
 		/// </summary>
-		bool PreLoadHeaderAndLength(HawkFile hawkFile);
+		bool PreLoadHeaderAndLength();
 		
 		/// <summary>
 		/// Gets the header key value pairs stored in the movie file

src/BizHawk.Client.EmuHawk/movie/PlayMovie.cs

@@ -136,7 +136,7 @@ namespace BizHawk.Client.EmuHawk
 
 			try
 			{
-				movie.PreLoadHeaderAndLength(hf);
+				movie.PreLoadHeaderAndLength();
 
 				// Don't do this from browse
 				if (movie.Hash == _game.Hash