blob endpoint removal after gloas

Remove `GET /eth/v1/beacon/blob_sidecars/{block_id}` and `blob_sidecar` event per ethereum/beacon-apis#577

Return 404 for all `GET /eth/v1/beacon/blobs/{block_id}` and remove all blob database code.

Start by locating the GET /eth/v1/beacon/blob_sidecars/{block_id} and GET /eth/v1/beacon/blobs/{block_id} handlers, the blob_sidecar event, and the blob database code. Verify the API behavior and related tests first; done means the old endpoint and event are removed, blob database code is gone, and requests to /eth/v1/beacon/blobs/{block_id} return 404.

Written by the indexing model from the issue text.