SCORU/Node: rely on cementation metadata for commitment

Context

The cementation operation cements the next possible commitment irrespective of the provided commitment hash for protocols >= Nairobi following !7316 (merged).

The rollup node used to look at the commitment hash field of the cement operation to ensure it agreed with what is cemented on L1. This discrepancy could cause the rollup node to believe something was wrong and stop.

We now also ignore it in the rollup node.

Manually testing the MR

dune exec tezt/tests/main.exe -- -f sc_rollup.ml -t 'Alpha: arith - rollup node - correct handling of commitments (cement_ignore_commitment)'
dune exec tezt/tests/main.exe -- -f sc_rollup.ml -t 'Nairobi: arith - rollup node - correct handling of commitments (cement_ignore_commitment)'