Removing the mention of the testnet portal from the migration doc

	modified:   docs/cloud/resources/migrate-to-portal-on-solana.mdx

Author: abernatskiy

docs/cloud/resources/migrate-to-portal-on-solana.mdx

@@ -140,7 +140,7 @@ pnpm install
 **A.** Replace all exising data sources with the portal:
 
 ```diff
-+  .setPortal('https://portal.tethys.sqd.dev/datasets/solana-beta')
++  .setPortal('https://portal.sqd.dev/datasets/solana-beta')
 -  .setGateway('https://v2.archive.subsquid.io/network/solana-mainnet')
 -  .setRpc({
 -    client: new SolanaRpcClient({