After libp2p (#268) is merged and we lose network compat anyway (PoC-2):

• Network message compatibility: Undo poc-1 message compat #277
• Use blobs in network messages: Pass around blobs on network rather than serde serialised rich types #265
• PoC-1 backwards compatibility #281 (justification format)
• PoC-1 backwards compatibility #291 (net version at 0)

After we restart the chain (PoC-3 probably):

• Sandbox externals in runtime WASM: Restore previous version of ext_sandbox_invoke #236
• Switch back to blake and remove tiny-keccak dep (source): Related: Exorcise RLP from codebase #664.
• Remove zero-padding for storage items. Zero-padding in storage should not be applied #347

Not relevant:

• Don't hash storage keys by default: Remove dependency on error_chain polkadot#270 (comment)