Remove language prefixes for llms.txt

Problem/Motivation

Currently when enabling the module on a multi-lingual website with language prefixes in the url, the llms.txt will also be prefixed with the langcode.
Example:
/en/llms.txt
/nl/llms.txt
/fr/llms.txt

The llms.txt file should by only accessible on the root-level: /llms.txt