Fix three terribly named variables

[karlfloersch]

There were a few terribly named variables that have been left around.

Just updating these names for a little added sanity -- there's a bunch more refactoring needed but this at least goes in the right direction towards a sane batch submitter.

[karlfloersch]

Update: Ugh. I'm a little unhappy about the fact that we have two types: Batch and SequenceTransactionBatch. Maybe these names require a bit more thought. At least we should absolutely change startsAtBatch which is just an utterly terrible name.

I'm down for either name for appendSequencerBatchParams or SequencerTransactionBatch. Let me know which y'all prefer and we can pick the relevant commit.

[tynes]

I like SequencerTransactionBatch more