We're exceeding our compute unit allotment with Neynar: [ENG-9930](https://linear.app/comm/issue/ENG-9930/exceeding-neynar-compute-units-due-to-fetchfarcasterchannelbyid).
It's mostly the `channel/search` API. I'm guessing it's more expensive than the `channel` API, which has fewer capabilities.
Turns out we actually already have `NeynarClient.fetchFarcasterChannelInfo`, which calls the `channel` API. But we don't have any callsites to it anymore.
This diff replaces the code for `NeynarClient.fetchFarcasterChannelByID` with `NeynarClient.fetchFarcasterChannelInfo`, and subsequently removes the latter.
This helps address [ENG-9930](https://linear.app/comm/issue/ENG-9930/excseeding-neynar-compute-units-due-to-fetchfarcasterchannelbyid).
Depends on D13978