Fix use of unaudited code in zksync-era

[edmundedgar]

We had to make a small change to support zksync-era which hasn't been audited (but should be fine) to replace the use of transfer which fails on zksync because it relies on hard-coded gas costs which don't apply on zk-sync.

Apparently zk-sync have a change in the pipeline that will make transfer work. If that ships we can redeploy with the standard version. We may need to do something to handle both versions in the UI if people are using it.

Alternatively, in the next version, replace the use of transfer and ship a version that works on all chains. We probably want to do this after Cancun as EIP-1153 makes reentrancy guards cheaper.