logcmdutil: remove unused attribute 'cache' from jsonchangeset printer

Perhaps it's a copy-pasta of changeset_templater at bd15932846a4.

mercurial/logcmdutil.py

@@ -317,7 +317,6 b' class jsonchangeset(changesetprinter):'
 
     def __init__(self, ui, repo, differ=None, diffopts=None, buffered=False):
         changesetprinter.__init__(self, ui, repo, differ, diffopts, buffered)
-        self.cache = {}
         self._first = True
 
     def close(self):