solana: Remove references to `payer.sequence_value` from the code comments

[johnsaigle]

This value was removed in #90 but is still listed as the seed for PDAs in e.g. https://github.com/wormhole-foundation/example-liquidity-layer/blob/f9d747b6e5439e3b3082d75a2daf697c0e53e2b2/solana/programs/token-router/src/processor/market_order/place_cctp.rs#L90-L110