Update prefilterrules.py -Fix insert before/after bug

Suspected Copy/Pasta issue from implementation in accessrules.py.  Bug fix for invalid url issues/ insert at wrong index in prefilter policies.

fmcapi/api_objects/policy_services/prefilterrules.py

@@ -102,7 +102,7 @@ def URL_SUFFIX(self):
         elif "insertAfter" in self.__dict__:
             url = f"{url}insertAfter={self.insertAfter}"
 
-        return url[:-1]
+        return url
 
     def parse_kwargs(self, **kwargs):
         """