feat!: Drop support for the legacy SSA

[TomAFrench]

Description

Problem*

Resolves

Summary*

This PR nukes the legacy SSA codebase so we only have the new ssa_refactor codebase. I've left it in the ssa_refactor directory to reduce the diff in this PR although this can be addressed in a followup PR.

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[TomAFrench]

This is necessary for stepwise ACVM / ACVM 0.21.0 as we have removed the Block, RAM and ROM opcodes. We would then need to either update the legacy SSA to not use these or remove it entirely.

[kevaundray]

For fully resolving #1850 -- Will leave that to @vezenovm and @jfecher

[vezenovm]

This looks good to me for a first removal. We can clean up remaining issues to fully resolve #1850 in later PRs.