Markov: this is kind of embarrassing. remove a duplicate index.

modules/Markov.py

@@ -124,6 +124,19 @@ class Markov(Module):
                 db.rollback()
                 print('sqlite error: ' + str(e))
                 raise
+        if (version < 4):
+            db = self.get_db()
+            try:
+                db.execute('''
+                    DROP INDEX markov_chain_key_index''')
+                db.execute('UPDATE drbotzo_modules SET version = ? WHERE module = ?',
+                    (4, self.__class__.__name__))
+                db.commit()
+                version = 4
+            except sqlite3.Error as e:
+                db.rollback()
+                print('sqlite error: ' + str(e))
+                raise
 
     def register_handlers(self):
         """Handle pubmsg/privmsg, to learn and/or reply to IRC events."""