Issue python#25505: Remove unused buggy method.

Author: terryjreedy

Tools/scripts/fixdiv.py

@@ -335,8 +335,6 @@ def readline(self):
         self.buffer.append(line)
         self.lineno += 1
         return line
-    def truncate(self):
-        del self.buffer[-window:]
     def __getitem__(self, index):
         self.fill()
         bufstart = self.lineno - len(self.buffer)