Remove ERC712 signing data as separate argument

[jtrein]

Expected behavior

We shouldn't allow for users to send their own sig + data to verify sig on POST message as this means they could technically send any previous signature and data. I only implemented this as a temporary stop-gap solution so I could quickly sign the same data the moloch v3 contracts expected.

We need to find a good way to allow Snapshot Hub and Moloch v3 to accept the same signatures (or something to that effect).

The dependencies of this being rectified is changing which data the user signs for Snapshot Hub and Moloch v3. Today, they see many hashed conversions of formerly readable text strings (e.g. name: "A Good Proposal" -> nameHash: "0x3de4....") which is not ideal.

Actual behavior

Users can send any sig + data to verify sig.

Steps to reproduce the behavior

Sign some proposal data in Tribute Dapp.

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cc: @adridadou @fforbeck