Remove Tab Index

Problem/Motivation

Tab index allows changing which tab order of the elements. This doesn't really make sense to be in the recaptcha global context. Let's just remove the functionality entirely. I had added it in the original module since it was part of the recaptcha API, but we don't need it.

Steps to reproduce

1. Install recaptcha
2. See tab index config option
3. Ponder why it exists

Proposed resolution

1. Remove tab index from the recaptcha module

Remaining tasks

* Merge the patch https://git.drupalcode.org/project/recaptcha/-/merge_requests/5

User interface changes

* Tab index is no longer an option

API changes

* Nothing

Data model changes

* tab-index be gone!