runtime: remove mmr and beefy from westend runtime (#2916)

* runtime: remove mmr and beefy from westend runtime

* runtime: westend: remove pallet_beefy config

* node: only start beefy gadget on rococo

* node: remove beefy keys from westend chain spec

polkadot/Cargo.lock

@@ -11190,7 +11190,6 @@ dependencies = [
  "pallet-authorship",
  "pallet-babe",
  "pallet-balances",
- "pallet-beefy",
  "pallet-collective",
  "pallet-democracy",
  "pallet-election-provider-multi-phase",
@@ -11200,7 +11199,6 @@ dependencies = [
  "pallet-im-online",
  "pallet-indices",
  "pallet-membership",
- "pallet-mmr",
  "pallet-mmr-primitives",
  "pallet-multisig",
  "pallet-nicks",