validateDataColumn: Remove error logs.

[nalepae]

What type of PR is this?
Other

What does this PR do? Why is it needed?
When we receive data column sidecars via gossip, if the sidecar does not respect the validation rules, a scary ERROR log is displayed. We can't to anything about it, since the error comes from an invalid incoming sidecar, so there is no need to print an ERROR message.

Node: As all REJECTED gossip message, a DEBUG log is also always displayed.

Example of ERROR log:

[2025-12-18 15:38:26.46] ERROR sync: Failed to decode message error=invalid ssz encoding. first variable element offset indexes into fixed value data
[2025-12-18 15:38:26.46] DEBUG sync: Gossip message was rejected agent=erigon/caplin error=invalid ssz encoding. first variable element offset indexes into fixed value data gossipScore=0 multiaddress=/ip4/141.147.32.105/tcp/9000 peerID=16Uiu2HAmHu88k97iBist1vJg7cPNuTjJFRARKvDF7yaH3Pv3Vmso topic=/eth2/c6ecb76c/data_column_sidecar_30/ssz_snappy

(After this PR, the DEBUG one will still be printed.)

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).

[kasey]

flawless 💎

[terencechain]

Lgtm