interfaces: drop the `raw` parameters on ifiledata interface

In practice it was not implemented since forever. The `rawdata` method fit that
purpose. The interface checking does not detect that because it seems to confuse
the `_df` argument for the `raw` one.

Dropping that `_df` argument in a descendant changesets revealed the issue.

mercurial/interfaces/repository.py

@@ -684,7 +684,7 b' class ifiledata(interfaceutil.Interface)'
         Any metadata is excluded from size measurements.
         """
 
-    def revision(node, raw=False):
+    def revision(node):
         """Obtain fulltext data for a node.
 
         By default, any storage transformations are applied before the data