[6.x] Remove webmozart/assert package

[miguilimzero]

Summary

This pull request removes the webmozart/assert package. The package is used in only one file to throw InvalidArgumentException in some scenarios. Although these exceptions are never caught, the PR manually adds the exceptions with the exact same messages from the package.

The motivation for this PR is because the package is giving some strange conflict errors when trying to install vimeo/psalm with socialstream and webmozart/asset with an already composer.lock generated.

Manually adding vimeo/psalm to the project and deleting the composer.lock fixes the conflict. However, since this package's last commit was 2 years ago and is only being used in one single file, I personally don't see a reason to keep it.

Checklist

• I've read this template
• I've checked reviewed this PR myself, ensuring consistency and quality with the rest of the project
• I've given a good reason as to why this PR exposes new / removes existing user data

[joelbutcher]

However, since this package's last commit was 2 years ago and is only being used in one single file, I personally don't see a reason to keep it.

Which commit / package are you referring to here?

[miguilimzero]

@joelbutcher https://github.com/webmozarts/assert package. The last commit was on Jun 3, 2022.