core/txpool, eth/catalyst: add API method to drop tracked txs from pools. prevent simulated beacon Rollback from reverting gas tip to 1 gwei.

[jwasinger]

This adds an API method DropTransactions to legacy pool, blob pool and txpool interface. This method removes all txs currently tracked in the pools.

It modifies the simulated beacon to use the new method in Rollback which removes previous hacky implementation that also erroneously reset the gas tip to 1 gwei.