[Wallet SDK] remove "scan proxy"

[PHOL-DA]

currently in the config.js we have:

const LOCALNET_SCAN_PROXY_API_URL = new URL(
    'http://wallet.localhost:2000/api/validator'
)

//scan proxy exposes the registry endpoints as well
const LOCALNET_REGISTRY_API_URL = new URL(
    LOCALNET_SCAN_PROXY_API_URL.href + '/v0/scan-proxy'
)

the LOCALNET_REGISTRY_API_URL is just a subset of the app validator so we should:

this is related to #802

just have one value (LOCALNET)_APP_VALIDATOR_URL and everywhere we use the scan proxy we just take this one with a post-fix.