Simplify html extension check

Simplified the check a bit here since `endswith` will cover the previous check and also I've removed the preceding `.` to make sure the old check is still covered.

lib/galaxy/datatypes/data.py

@@ -369,7 +369,7 @@ class Data(metaclass=DataMeta):
         """
         rel_paths = []
         file_paths = []
-        if dataset.datatype.composite_type or dataset.extension == '.html' or dataset.extension.endswith('.html'):
+        if dataset.datatype.composite_type or dataset.extension.endswith('html'):
             main_file = f"{name}.html"
             rel_paths.append(main_file)
             file_paths.append(dataset.file_name)