revlog: make the `candelta` method private

It is only used internally, so lets make it clear.

mercurial/revlog.py

@@ -894,7 +894,7 b' class revlog:'
         except KeyError:
             return False
 
-    def candelta(self, baserev, rev):
+    def _candelta(self, baserev, rev):
         """whether two revisions (baserev, rev) can be delta-ed or not"""
         # Disable delta if either rev requires a content-changing flag
         # processor (ex. LFS). This is because such flag processor can alter
@@ -3105,7 +3105,7 b' class revlog:'
             nodesorder,
             revlogrevisiondelta,
             deltaparentfn=self.deltaparent,
-            candeltafn=self.candelta,
+            candeltafn=self._candelta,
             rawsizefn=self.rawsize,
             revdifffn=self.revdiff,
             flagsfn=self.flags,

tests/test-revlog-raw.py

@@ -158,7 +158,7 b" def addgroupcopy(rlog, tr, destname=b'_d"
             else:
                 # suboptimal deltaparent
                 deltaparent = min(0, parentrev)
-            if not rlog.candelta(deltaparent, r):
+            if not rlog._candelta(deltaparent, r):
                 deltaparent = -1
             return {
                 b'node': rlog.node(r),