Remove public_key args from create_conditional_escrow

[netpoe]

Currently, we have this rule:

        if let Some(key) = public_key {
            promise = promise.add_full_access_key(key.into())
        }

Making public_key a mandatory arg to create_conditional_escrow function.

If users are to create Function Call proposals from the NEAR Holdings DAO, this arg makes it difficult for the proposer to get the public_key value, etc.

Refactor

Update the code, so that we use: env::signer_account_pk: https://docs.rs/near-sdk/latest/near_sdk/env/fn.signer_account_pk.html

[susguzman]

Agree!