[docs] Remove validator set change query from block_search endpoint examples

[dasanchez]

Hi! The block_search endpoint has examples listed here:

• https://github.com/cometbft/cometbft/blob/main/docs/guides/app-dev/indexing-transactions.md#querying-block-events
• https://docs.cometbft.com/v0.37/rpc/#/Info/block_search

They list both a val_set.num_changed > 0 and a valset.changed > 0 query, but neither seems to work with Gaia v17.2.0 (CometBFT v0.37.6).
Are these queries still active, or have they been deprecated?

A delegation went through at height 6884760 in the ICS testnet, triggering a valset change:

curl -s "https://rpc.provider-sentry-01.ics-testnet.polypore.xyz/block_results?height=6884760" | jq '.result.validator_updates | length'
1

If I try to search for that block using the valset.changed>0 query with block_search, I don't get the 6884760 block in the results:

curl -s "https://rpc.provider-sentry-01.ics-testnet.polypore.xyz/block_search?query=\"block.height>6884759%20AND%20block.height<6884761\"" | jq '.result.total_count' 
"1"

curl -s "https://rpc.provider-sentry-01.ics-testnet.polypore.xyz/block_search?query=\"block.height>6884759%20AND%20block.height<6884761%20AND%20valset.changed>0\"" | jq '.result.total_count'
"0"

Thanks!