fix(staking): disable Asset Hub nomination-pools until wallet supports Polkadot 2.0

- Asset Hub HEZ staking set to null (was nomination-pools)
- Relay chain HEZ keeps relaychain staking only
- Wallet code prepared for Polkadot 2.0 but config disabled for now

pezkuwi-overlay/chains/pezkuwi-chains.json

@@ -129,9 +129,7 @@
         "precision": 12,
         "name": "Hezkurd",
         "priceId": "hezkurd",
-        "staking": [
-          "nomination-pools"
-        ],
+        "staking": null,
         "type": "native",
         "icon": "https://raw.githubusercontent.com/pezkuwichain/pezkuwi-wallet-utils/main/icons/tokens/HEZ.png",
         "buyProviders": {},