Use native ntlk download (#3796)
This PR changes how we download NLTK data to use the native nltk
downloader.
We had moved to our own hosted NLTK dataset because of this CVE:
https://nvd.nist.gov/vuln/detail/CVE-2024-39705
Ref: https://github.com/Unstructured-IO/unstructured/pull/3361
Latest versions of NLTK have fixed this issue:
https://github.com/nltk/nltk/blob/develop/ChangeLog
