Activate PeerDAS at Fulu Fork and remove `EIP7594_FORK_EPOCH`

[jimmygchen]

Description

The initial Fulu spec was merged in ethereum/consensus-specs#3994, and EIP7594_FORK_EPOCH and EIP7594_FORK_VERSION no longer exists in the configuration; The spec now specifies PeerDAS to be activated at FULU_FORK_EPOCH.

We'll need to change PeerDAS activation to happen at the Fulu fork in Lighthouse, and remove the eip7594 related configurations. There is a WIP PR for the Fulu fork boiler plate, and is required for this task.

[jimmygchen]

#6695 merged \o/ This is unblocked.