[0.15] Remove legacy event handler

[icebob]

:memo: Description

This PR removed the legacy event handler signature.

:gem: Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

:scroll: Example code

Legacy event handler

module.exports = {
    name: "accounts",
    events: {
        "user.created"(payload, sender, eventName) {
            // ...
        }
    }
};

Supported event handler

module.exports = {
    name: "accounts",
    events: {
        "user.created"(ctx) {
            console.log("Payload:", ctx.params);
            console.log("Sender:", ctx.nodeID);
            console.log("We have also metadata:", ctx.meta);
            console.log("The called event name:", ctx.eventName);

            // ...
        }
    }
};

:vertical_traffic_light: How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] Test A
• [ ] Test B

:checkered_flag: Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] I have commented my code, particularly in hard-to-understand areas