Adds the deploy config for sepolia. Also clean up a little
bit of dead code and parse sepolia L1 and L2 in the deployer
script. Optimistic Kovan had a chain id of 69 and is now deprecated,
so re-using 69 for Optimistic Sepolia so that 420 can be used
by goerli still while both goerli and sepolia run in parallel.

To review the deploy config, the values should all match goerli
except for the eip 1559 params which should now match mainnet.
The chainids should also be different.