sidedata: use the "feature" to detect that sidedata are enabled

This is more versatile than relying on the revlogv2 requirements.

Differential Revision: https://phab.mercurial-scm.org/D10657

mercurial/localrepo.py

@@ -3372,7 +3372,7 b' class localrepository(object):'
         return self.pathto(fp.name[len(self.root) + 1 :])
 
     def register_wanted_sidedata(self, category):
-        if requirementsmod.REVLOGV2_REQUIREMENT not in self.requirements:
+        if repository.REPO_FEATURE_SIDE_DATA not in self.features:
             # Only revlogv2 repos can want sidedata.
             return
         self._wanted_sidedata.add(pycompat.bytestr(category))