revert paritytech/polkadot#6577 & related changes (paritytech#3108)

Moves `pallet_mmr` back behind `pallet_session` to address
polkadot-fellows/runtimes#160.

Opening draft for CI - should be merged or closed depending on outcome
of w3f/polkadot-spec#718.

---------

Co-authored-by: Adrian Catangiu <[email protected]>

substrate/bin/node/runtime/src/lib.rs

@@ -2099,11 +2099,6 @@ construct_runtime!(
 		AssetConversionTxPayment: pallet_asset_conversion_tx_payment,
 		ElectionProviderMultiPhase: pallet_election_provider_multi_phase,
 		Staking: pallet_staking,
-		Beefy: pallet_beefy,
-		// MMR leaf construction must be before session in order to have leaf contents
-		// refer to block<N-1> consistently. see substrate issue #11797 for details.
-		Mmr: pallet_mmr,
-		MmrLeaf: pallet_beefy_mmr,
 		Session: pallet_session,
 		Democracy: pallet_democracy,
 		Council: pallet_collective::<Instance1>,
@@ -2133,6 +2128,11 @@ construct_runtime!(
 		Tips: pallet_tips,
 		Assets: pallet_assets::<Instance1>,
 		PoolAssets: pallet_assets::<Instance2>,
+		Beefy: pallet_beefy,
+		// MMR leaf construction must be after session in order to have a leaf's next_auth_set
+		// refer to block<N>. See issue polkadot-fellows/runtimes#160 for details.
+		Mmr: pallet_mmr,
+		MmrLeaf: pallet_beefy_mmr,
 		Lottery: pallet_lottery,
 		Nis: pallet_nis,
 		Uniques: pallet_uniques,