fix: remove user discriminator

[Mittelblut9]

Description

Removed all references with discriminator

Motivation and Context

Due Discord's new Update, the well-known discriminator (#2444) will be gone, which will be released in the next weeks.

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[twlite]

🤔 I think we should have a place for @usernames though. We are planning to redesign this entire lib from scratch, but I am going to keep this pr open for now as a reference.

Removing this entirely would break a lot of projects out there. Could we just conditionally render it instead of removing it completely? @Mittelblut9

[twlite]

https://github.com/neplextech/canvacord/releases/tag/v5.4.9