Convert Critical request chains to use lantern LCP graph

[connorjclark]

it's the new cool kid on the block, he moved in years ago but crc hasn't said hi yet, rude.

[patrickhulce]

The remaining work left here would be converting the critical request chains audit from surfacing "requests issued with high priority" to "requests that we thought contributed to LCP". It's a relatively low priority fix though, so I'm unassigning and returning to the pool of available work if anyone is particularly interested in picking this up.

The work in CRC computed artifact itself is really quite small now that the graph refactor is done (mostly deleting code and using the LCP graph to build the CRC artifact instead of the entire graph).