fix(account-lib): remove message whitelist for cold and custody wallets

[bhavidhingra]

TICKET: COIN-6527

This pull request simplifies the message verification logic in the modules/account-lib/src/index.ts file by removing redundant validation and unused imports. The most important changes are:

Message verification logic:

• The verifyMessage function now only checks the validity of the encoded payload using verifyEncodedPayload, removing the additional call to validateAgainstMessageTemplates. This streamlines the verification process and avoids redundant checks.

Code cleanup:

• The unused validateAgainstMessageTemplates import was removed from the file, as it is no longer needed after the above change.

[akarath]

Approved