Remove web3._utils.formatters in favor of eth-utils versions

[pipermerriam]

Depends on #1195 which upgrades the eth-utils dependency

What was wrong?

https://github.com/ethereum/web3.py/blob/864bc1d2a93ba7a6ca2a0629839b0d7a4c944e12/web3/_utils/formatters.py

We currently have a module web3._utils.formatters which implements a number of functional formatter functions. These functions were elevated to live in eth-utils recently and thus are duplicate code.

How can it be fixed?

Remove any/all functions from web3._utils.formatters in favor of the eth-utils versions.

[dylanjw]

Can I include this change in #1209? It might be the same amount of work to do as it would to rebase this change from master.

[pipermerriam]

If they can be done separately that would be ideal since this change should just be code removal and modification of imports. Mixing that with functionality changes makes for more difficult review. Feel free to write them together but to segregate your commits so that when you're done you can split them into two PRs.