Remove Sum Tree codebase

[bvrooman]

Related issues:

• Untracked

This PR removes the Binary Merkle Sum Tree since it is deprecated and not used. Removing the BMST will reduce the overall codebase complexity and improve readability.

Because this removes public facing types, this is a breaking change. However, it is safe in the context of fuel-core since the BMST was never used.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• If performance characteristic of an instruction change, update gas costs as well or make a follow-up PR for that
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

[Add or remove entries as needed]

• Rust SDK
• Sway compiler
• Platform documentation (for out-of-organization contributors, the person merging the PR will do this)
• Someone else?