Remove dependency on the ic-crypto-standalone-sig-verifier (#2586)

This PR removes the `ic-crypto-standalone-sig-verifier` dependency,
because it was one of the last dependency that II had on the ic
repository. There are now properly published alternatives available
(also maintained by the crypto team).

However, the published package only supports canister signatures at the
moment, the feature set of `sig-verifier-js` is reduced to only
verifying canister signatures too. This is sufficient to integrate with
II in a web2 context (which is what this library was initially intended
for).