Add coverage for unsupported keyring methods

[mikesposito]

Explanation

This PR adds some test coverage for cases where the requested method is not supported by the keyring linked with the provided account. These are the methods tested:

• removeAccount
• exportAccount
• getEncryptionPublicKey
• decryptMessage
• signMessage
• signPersonalMessage
• signTypedMessage
• signTransaction

The remaining methods related to user operations will be addressed in another PR, as they also need more refactoring to be aligned with how tests for other methods are written.

References

• Related to Merge EthKeyringController into KeyringController #3830

Changelog

No documentable changes

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate

[mcmire]

Looks good!