chore: remove unused path of code

There seems to be [an unused, left-over path of code](https://github.com/jmespath-community/python-jmespath/blob/8211b50f33ff7f327dc5742b797ee5cbf1d1b119/jmespath/parser.py#L197) that will never trigger.
Please, consider removing that code.

FYI: see [corresponding fix](https://github.com/jmespath-community/typescript-jmespath/pull/54) in TypeScript implementation.
