.Net: Removed Kernel events

[dmytrostruk]

Motivation and Context

Related: https://github.com/microsoft/semantic-kernel/issues/9499

Removed the usage of obsolete Kernel Events in favor of Filters as part of Filters graduation process.

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• [x] All unit tests pass, and I have added new tests where possible
• [x] I didn't break anyone :smile: