Remove direct calls to public functions

[spalladino]

Summary of changes:

• Removed the PrivateTx and PublicTx subtypes for Tx.
• Removed the txRequest from a Tx, which was used to indicate a topmost public function call.
• Removed SignedTx and SignedTxRequest types.
• Removed public kernel with no previous kernel circuit and input struct.

Fixes #663

[spalladino]

cc @PhilWindle to remove skip when 662 is ready. Will require tweaking this bit as well:

aztec-packages/yarn-project/end-to-end/src/utils.ts

Lines 71 to 79 in 72524f8

	if (i == 0) {
	// TODO(#662): Let the aztec rpc server generate the keypair rather than hardcoding the private key and generate all accounts as smart accounts
	const [txHash, newAddress] = await aztecRpcServer.createSmartAccount(privateKey);
	const isMined = await new SentTx(aztecRpcServer, Promise.resolve(txHash)).isMined();
	expect(isMined).toBeTruthy();
	address = newAddress;
	} else {
	address = await aztecRpcServer.addExternallyOwnedAccount();
	}

[PhilWindle]

A lot of changes but the general gist is fantastic. So much extraneous complexity ripped out. It must have been cathartic.

[PhilWindle]

The simplifications in this file alone make me much happier!