revlog: remove legacy usage of `_withsparseread`

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

contrib/perf.py

@@ -3983,7 +3983,13 b' def perfrevlogrevision(ui, repo, file_, '
 
     size = r.length(rev)
     chain = r._deltachain(rev)[0]
-    if not getattr(r, '_withsparseread', False):
+
+    with_sparse_read = False
+    if hasattr(r, 'data_config'):
+        with_sparse_read = r.data_config.with_sparse_read
+    elif hasattr(r, '_withsparseread'):
+        with_sparse_read = r._withsparseread
+    if with_sparse_read:
         slicedchain = (chain,)
     else:
         slicedchain = tuple(slicechunk(r, chain, targetsize=size))
@@ -4000,7 +4006,7 b' def perfrevlogrevision(ui, repo, file_, '
         (lambda: doread(chain), b'read'),
     ]
 
-    if getattr(r, '_withsparseread', False):
+    if with_sparse_read:
         slicing = (lambda: doslice(r, chain, size), b'slice-sparse-chain')
         benches.append(slicing)
 

mercurial/debugcommands.py

@@ -806,7 +806,7 b' def debugdeltachain(ui, repo, file_=None'
     start = r.start
     length = r.length
     generaldelta = r.delta_config.general_delta
-    withsparseread = getattr(r, '_withsparseread', False)
+    withsparseread = r.data_config.with_sparse_read
 
     # security to avoid crash on corrupted revlogs
     total_revs = len(index)

mercurial/revlog.py

@@ -2021,7 +2021,7 b' class revlog:'
         l = []
         ladd = l.append
 
-        if not self._withsparseread:
+        if not self.data_config.with_sparse_read:
             slicedchunks = (revs,)
         else:
             slicedchunks = deltautil.slicechunk(