Simplify MovieSession a bit

src/BizHawk.Client.Common/movie/MovieService.cs

@@ -17,12 +17,6 @@ namespace BizHawk.Client.Common
 			return new Bk2Movie(path);
 		}
 
-		/// <summary>
-		/// Creates a standard <see cref="IMovie"/> instance, 
-		/// no path is specified so this is in a minimal state that would not be able to be saved
-		/// </summary>
-		public static IMovie Create() => new Bk2Movie();
-
 		/// <summary>
 		/// Creates a <see cref="ITasSession"/> instance
 		/// </summary>

src/BizHawk.Client.Common/movie/MovieSession.cs

@@ -37,7 +37,7 @@ namespace BizHawk.Client.Common
 			_modeChangedCallback = modeChangedCallback
 				?? throw new ArgumentNullException($"{nameof(modeChangedCallback)} CannotUnloadAppDomainException be null.");
 
-			Movie = MovieService.Create();
+			Movie = new Bk2Movie();
 		}
 
 		public IMovie Movie { get; private set; }