Relay v1.6.1: added support for bridge-hub-kusama/1002004 + aligned...

Relay v1.6.1: added support for bridge-hub-kusama/1002004 + aligned kusama/1002004, P to polkadot/1002000 (#3007)

* Adjusted KBH version

* Removed unused files

* Updated RELEASE.md

* Align relaychains (Kusama, Polkadot)

* fmt

* Fix import

* leave also before

* Use latest subxt-codegen