Remove babel from CLI

[spalladino]

The CLI depends on web3-provider-engine, which requires json-rpc-engine, which bundles babel as dependency.

We are currently using web3-provider-engine only to manually inject a NonceTracker to an hdwallet-provider if present, due to this issue. See #586 for a recent occurrence of that problem in zos.

See if we can work this around by including only what we strictly need from provider-engine, to avoid importing json-rpc-engine at all. Another option would be to check if the issue in hdwallet-provider is fixed, and just suggest our users to upgrade if we detect they are using an old version.