Remove SyncHeaders

[colin-axner]

I never understood the exact purpose of SyncHeaders, but I realize now it is just a cache of the latest headers for each chain id ie a cache with a depth of 1 per chain-id. Sync makes sense in this context, but it doesn't make sense until you know what it does, stating the structure to be a cache of headers will make more sense imo

[colin-axner]

Alternatively, I'd be in favor of outright removing this structure. We really should just be interacting with the trusted store of the tendermint light client. It doesn't make much sense to keep a cache of one header, I don't even know a location where we benefit from this

[colin-axner]

I'll be removing them, my refactor of the light clients greatly reduces the complexity here. We simply can either update the off chain light client or get a header to update the on chain light client