revlog: remove legacy usage of `_lazydeltabase`

All core code is now getting the setting from the DeltaConfig object.

contrib/perf.py

@@ -3549,7 +3549,10 b' def _timeonewrite('
     timings = []
     tr = _faketr()
     with _temprevlog(ui, orig, startrev) as dest:
-        dest._lazydeltabase = lazydeltabase
+        if hasattr(dest, "delta_config"):
+            dest.delta_config.lazy_delta_base = lazydeltabase
+        else:
+            dest._lazydeltabase = lazydeltabase
         revs = list(orig.revs(startrev, stoprev))
         total = len(revs)
         topic = 'adding'

mercurial/revlogutils/deltas.py

@@ -1177,7 +1177,7 b' class deltacomputer:'
                 and self.revlog.length(currentbase) == 0
             ):
                 currentbase = self.revlog.deltaparent(currentbase)
-            if self.revlog._lazydelta and currentbase == base:
+            if self.revlog.delta_config.lazy_delta and currentbase == base:
                 delta = revinfo.cachedelta[1]
         if delta is None:
             delta = self._builddeltadiff(base, revinfo)