Remove CCID from CCGN website

## Problem
CCID has many issues and we are in a place where we can just remove it. I'd list some of those issues
- [RubyCas](https://github.com/rubycas/rubycas-server) (the server behind [CCID](https://github.com/creativecommons/CCID-cas)) is abandoned (the last commit was 2015-12-09) so that is a potential security risk
- creativecommons/commoners: [`plugins/cas-maestro`](https://github.com/creativecommons/commoners/tree/master/plugins/cas-maestro) is the WordPress plugin for the Single Sign On process is a modified version of this [CAS Maestro](https://github.com/vaurdan/cas-maestro) plugin which hasn't been updated since 2014-11-04, this is a potential security risk and an eventual compatibility problem with the newest WordPress versions
- We have deprecated CCID integration:
- CCID integration with CreativeCommons.org was removed 2022-02-09
- CCID integration with wiki.creativecommons.org removal TBD
- There's a lot of issues related to CCID problems
- https://github.com/creativecommons/commoners/issues/339
- https://github.com/creativecommons/commoners/issues/408
- https://github.com/creativecommons/commoners/issues/424
- https://github.com/creativecommons/commoners/issues/436
- https://github.com/creativecommons/commoners/issues/438

## Process
Removing CCID will involve:
- Checking user workflow to check if `login.creativecommons.org` is hardcoded in the [Global Network plugin](https://github.com/creativecommons/wp-plugin-cc-global-network)
- Sending notification to CCGN users regarding upcoming password change
- Removing WordPress Plugin
- Sending notification to CCGN users to update their passwords

## Additional context
@Juliabrungs told me this is also an opportunity to check how many active users we currently have

## Implementation

- [x] I would be interested in implementing this feature.