bug/1329: Extension - Chain validation sometimes fails

[jurevans]

As the extension only needs to know the chainId in order to validate signing requests, remove complex chain config and the associated validation (this is causing issues where old versions of the extension cannot update, and breaks the App popup!)

• Simply chain service, only track chain ID
• Remove unused Namada calls for getChain, etc.
• Remove any other unused items
• Fix any broken tests

Testing

• Simply load this version if you're already running a local dev extension - it should gracefully update to the new storage and not throw any errors!
• To test signing, until feat/1295 - Update Namada Keychain integration #1298 is merged, you'll have to set the Network chain ID again, since it will revert to a default value

TODO

• The chainService should be completely deprecated when we have the permissions updates in WIP - feat/1078: Extension: Permission improvements #1142 - once that is update, chain service will no longer be needed!

[pedrorezende]

Very good refactor! 🥇