Fix memfile undo decoding creating undo steps

Exiting modes shouldn't be needed since loading the new memfile
will free the old data.

Sculpt mode dynamic topology was adding undo data on exiting the mode
which isn't logical in this case and can be avoided altogether.

source/blender/editors/undo/memfile_undo.c

@@ -82,9 +82,6 @@ static bool memfile_undosys_step_encode(struct bContext *C, UndoStep *us_p)
 
 static void memfile_undosys_step_decode(struct bContext *C, UndoStep *us_p, int UNUSED(dir))
 {
-	/* Loading the content will correctly switch into compatible non-object modes. */
-	ED_object_mode_exit(C);
-
 	MemFileUndoStep *us = (MemFileUndoStep *)us_p;
 	BKE_memfile_undo_decode(us->data, C);