Update stale naming of hashes and clean up hash functions in `L2Block`

[benesjan]

With the changes for message boxed related to #4492, we no longer just have one commitment to data.

To improve clarity, the current calldataHash is replaced with txs_effects_hash (formerly known as txs_hash).

Furthermore, some of the hashing functionality of the L2Block is now stale and unused, and therefore be removed.

Look for "TODO(#4844)" in the codebase.