Remove dependency on Asdf::Tool* classes

Overview

We have three classes related to asdf and managing tool versions: Asdf::ToolVersions Asdf::ToolVersion & Asdf::Tool.

The majority of this functionality has been replaced by GDK::ToolVersionsUpdater but there are a few remaining places that still use these classes.

Most of the dependency on these classes will be removed by #2923 (closed)

This issue is to remove the remaining usage and delete the classes.

Proposal

• Move functionality of Asdf::ToolVersions.default_version_for into GDK::ToolVersionsUpdater
• Replace invocations of default_version_for with new method.
• Remove any other related code to Asdf::Tool* classes.
• Delete the classes & tests.