Function decrease_validator_stake_with_vote 

pub fn decrease_validator_stake_with_vote(
    program_id: &Pubkey,
    stake_pool: &StakePool,
    stake_pool_address: &Pubkey,
    vote_account_address: &Pubkey,
    lamports: u64,
    validator_stake_seed: Option<NonZeroU32>,
    transient_stake_seed: u64,
) -> Instruction

Create a DecreaseValidatorStake instruction given an existing stake pool and vote account