changelog: stop useless enforcing split at the end of transaction

Changelogs are no longer created inline, and existing changelogs are
automatically split. Since we now enforce splitting at the start of any write,
we don't need to enforce splitting at the end of the transaction.

This has the nice side effect of killing the only user of "side_write".

mercurial/changelog.py

@@ -369,8 +369,9 b' class changelog(revlog.revlog):'
         else:
             new_index_file = self._inner.finalize_pending()
             self._indexfile = new_index_file
-            # split when we're done
-            self._enforceinlinesize(tr, side_write=False)
+            if self._inline:
+                msg = 'changelog should not be inline at that point'
+                raise error.ProgrammingError(msg)
 
     def _writepending(self, tr):
         """create a file containing the unfinalized state for