chore: remove events mixin.

[matthewhartstonge]

Moves the functionality from the events mixin into the focusable mixin, the only place it was used.

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[github-actions[bot]]

Some tests with 'continue-on-error: true' have failed:

• ember-canary

  • ember-beta
  • embroider-optimized
  • embroider-safe

  Created by continue-on-error-comment