bpo-32989: IDLE - remove unneeded parameter  (GH-18138)

IDLE does not pass a non-default _synchre in any of its calls to
pyparse.find_good_parse_start.
diff --git a/Lib/idlelib/pyparse.py b/Lib/idlelib/pyparse.py
index 9fa2010..d34872b 100644
--- a/Lib/idlelib/pyparse.py
+++ b/Lib/idlelib/pyparse.py
@@ -133,7 +133,7 @@
         self.code = s
         self.study_level = 0
 
-    def find_good_parse_start(self, is_char_in_string, _synchre=_synchre):
+    def find_good_parse_start(self, is_char_in_string):
         """
         Return index of a good place to begin parsing, as close to the
         end of the string as possible.  This will be the start of some