[XCMv5]Remove XCM testnet NetworkIds (#5390)

# Context
Close #5241, for more detail, please refer to
[RFC0108](https://github.com/polkadot-fellows/RFCs/pull/108)
# Changes
- Remove `Rococo` and `Westend` from `NetworkId`
* Add `Rococo Genesis Hash` and `Westend Genesis Hash`

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Co-authored-by: Nazar Mokrynskyi <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Adrian Catangiu <[email protected]>
Co-authored-by: Francisco Aguirre <[email protected]>