refactor!: use maybeGetSemaphoreSnarkArtifacts from `@zk-kit/utils

[sripwoud]

Description

This PRs uses the maybeGetSemaphoreSnarkArtifacts function added in privacy-scaling-explorations/zk-kit#240.
It deletes code that becomes unnecessary in @semaphore-protocol/proof.

Notes about docs:

• v4: I haven't found any reference to artifacts in the docs, so no changes to do
• v3: there is a reference to a download-snark-artifacts.ts script file, didn't do any changes there either as this PR impacts v4 only

Breaking change

Change	Before	After
SnarkArtifacts keys (optional param of generateProof)	{ wasmFilePath, zkeyFilePath }	{ wasm, zkey }

Related Issue(s)

Closes #746

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have run yarn prettier and yarn lint without getting any errors
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[cedoor]

@sripwoud this PR introduces a breaking change (the SnarkArtifacts type has different property names). Worth mentioning it.

[sripwoud]

@sripwoud this PR introduces a breaking change (the SnarkArtifacts type has different property names). Worth mentioning it.

Done. Update PR title and description