Move the testing library to rust-SCs repository

[Bargsteen]

Purpose

Moving the testing library to the rust SCs repository: Concordium/concordium-rust-smart-contracts#336
This PR removes it from the tools repository.

Changes

• Delete the testing library
• Replace the rust-sdk submodule with base as it was only the testing lib that needed the rust-sdk
• Update paths to use base instead of the rust-sdk
• Delete release tags for testing library once this is merged.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.