Stop running proteustestnet agents (#2794)

### Description

- Rpc urls are super flaky, stopping the validators and relayer support
- Keeping proteustestnet artifacts / chain metadata for now

### Drive-by changes

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### Related issues

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- Fixes #[issue number here]
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### Backward compatibility

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implications, e.g. changes that would prohibit deploying older commits
using this infra tooling?

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### Testing

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typescript/infra/config/environments/testnet3/agent.ts

@@ -118,9 +118,6 @@ const hyperlane: RootAgentConfig = {
       [chainMetadata.solanadevnet.name]: {
         tag: '79bad9d-20230706-190752',
       },
-      [chainMetadata.proteustestnet.name]: {
-        tag: 'c7c44b2-20230811-133851',
-      },
     },
     chains: validatorChainConfig(Contexts.Hyperlane),
   },

typescript/infra/config/environments/testnet3/chains.ts

@@ -42,11 +42,7 @@ export const ethereumChainNames = Object.keys(
 
 export const environment = 'testnet3';
 
-const validatorChainNames = [
-  ...supportedChainNames,
-  chainMetadata.proteustestnet.name,
-];
-
+const validatorChainNames = supportedChainNames;
 const relayerChainNames = validatorChainNames;
 
 export const agentChainNames: AgentChainNames = {