Description

Closes: #566

This PR removes all legacy handlers since it is no longer used.

See: cosmos/cosmos-sdk#7517

Author Checklist

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I have...

• included the correct type prefix in the PR title
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• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
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• confirmed the correct type prefix in the PR title
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• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)