Remove Classy dependency

Problem/Motivation

Recently, when checking for D11 changes required, it was discovered that Classy:^1.0 is not available for D11.

Steps to reproduce

composer update drupal/boldy

Proposed resolution

While we can update Classy to ^2.0, this issue will need to continue to be fixed in the future.
As per: https://www.drupal.org/node/3305674 →
We can remove the need to have Classy installed, remove the missing libraries, and add them to Boldy.

Remaining tasks

Check https://www.drupal.org/node/3305674 → for the requirements to remove the requirement, then implement those changes.