[cumulus] parachains-common testnet constants cleaning (#3134)

The `parachains-common` contains a lots of constants and type
definitions which are used for `polkadot-sdk`'s testnet runtimes and
also for `polkadot-fellows`'s production [SP
runtimes](https://github.com/polkadot-fellows/runtimes/tree/main/system-parachains/constants).
This PR cleans `parachains-common` module to contain only common and
generic functionality.

Testnet-specific constants have been moved to the separate module
dedicated just for testnets:
`polkadot-sdk/cumulus/parachains/runtimes/constants/`


Part of: https://github.com/paritytech/polkadot-sdk/issues/3054

---------

Co-authored-by: georgepisaltu <george.pisaltu@parity.io>

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-rococo/tests/tests.rs

@@ -27,10 +27,7 @@ use bridge_hub_rococo_runtime::{
 use bridge_hub_test_utils::SlotDurations;
 use codec::{Decode, Encode};
 use frame_support::{dispatch::GetDispatchInfo, parameter_types, traits::ConstU8};
-use parachains_common::{
-	rococo::{consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, fee::WeightToFee},
-	AccountId, AuraId, Balance, SLOT_DURATION,
-};
+use parachains_common::{AccountId, AuraId, Balance, SLOT_DURATION};
 use snowbridge_core::ChannelId;
 use sp_consensus_aura::SlotDuration;
 use sp_core::H160;
@@ -39,6 +36,9 @@ use sp_runtime::{
 	generic::{Era, SignedPayload},
 	AccountId32,
 };
+use testnet_parachains_constants::rococo::{
+	consensus::RELAY_CHAIN_SLOT_DURATION_MILLIS, fee::WeightToFee,
+};
 use xcm::latest::prelude::*;
 
 parameter_types! {