[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/integration-tests/emulated/tests/assets/asset-hub-westend/Cargo.toml

@@ -32,6 +32,7 @@ westend-runtime = { path = "../../../../../../../polkadot/runtime/westend" }
 
 # Cumulus
 parachains-common = { path = "../../../../../../parachains/common" }
+testnet-parachains-constants = { path = "../../../../../runtimes/constants", features = ["westend"] }
 asset-hub-westend-runtime = { path = "../../../../../runtimes/assets/asset-hub-westend" }
 asset-test-utils = { path = "../../../../../runtimes/assets/test-utils" }
 cumulus-pallet-xcmp-queue = { default-features = false, path = "../../../../../../pallets/xcmp-queue" }

cumulus/parachains/integration-tests/emulated/tests/assets/asset-hub-westend/src/tests/mod.rs

@@ -26,5 +26,5 @@ emulated_integration_tests_common::include_penpal_create_foreign_asset_on_asset_
 	PenpalB,
 	AssetHubWestend,
 	WESTEND_ED,
-	parachains_common::westend::fee::WeightToFee
+	testnet_parachains_constants::westend::fee::WeightToFee
 );