Avoid double verification of DataColumnSidecars in simple Sampler

[zilm13]

Data availability check in ForkChoice should ensure:

• Sidecar was seen and we were able to download it
• kzg proof verification is passed for it

For any custody sidecar in DB:

• we were able to download it
• kzg verification was run (at least for incoming sidecars, clarify for block where we were a proposer)

So for simple Sampler in Forkchoice we don't need to get it from DB and run kzg verification. We should only check that DataColumnSidecarIdentifier exists in DB in ForkChoice.