[OP] chore: remove unused activated_height

[bap2pecs]

Summary

after babylonlabs-io/finality-provider#42, we no longer need to read activated height from the cw contract.

instead, we properly find the time when the first delegation became active (see babylonchain/finality-provider#432)

so this cleans up the unused field

Test Plan

cargo optimize
cargo precommit
cargo integration
cargo test