Noir contract examples: don't emit unencrypted logs from private functions!

[iAmMichaelConnor]

Emitting an unencrypted log from a private function removes all of the 'function hiding' properties that the Aztec architecture strives for. It's 'bad practice' that oughtn't be exemplified.

Please remove these logs :)

Hopefully the example apps don't 'subscribe' to unencrypted logs in any way.

Example:

aztec-packages/yarn-project/noir-contracts/src/contracts/private_token_contract/src/main.nr

Line 89 in a78d939

emit_unencrypted_log(&mut context, "Coins transferred");

[iAmMichaelConnor]

Request: don't do this fix for the private_token_contract, but we should add a note to getting started guide to say this is leaky (and point to 'best practices' page). AND put a warning in the source code.