Review beacon api routes and remove no longer supported apis

[nflaig]

There should be a few routes we can remove from the code as those are no longer part of beacon api spec. There is no good reason to keep them around as they are unused and replaced by more forward compatible apis (v2).

E.g. getState (v1) has been removed from spec a while ago

lodestar/packages/api/src/beacon/routes/debug.ts

Line 120 in 8b59f50

getState: Endpoint<

This should be done after #6749 is merged to avoid conflicts.