Update subgraph request google doc

[mkflow27]

https://docs.balancer.fi/data-and-analytics/data-and-analytics/dune/dashboards.html the link to the request google doc is outdated. Let'S either renew it or remove the request part.

From the link checker report also:
[404] https://github.com/duneanalytics/spellbook/tree/main/models/balancer | Network error: Not Found
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