fix(typings): Fix Preboot Typings to accept multiple events.

[josephliccini]

• The current behavior is that the "events" and "keycodes" property are allowed an array of one item.
• The new behavior is that these properties now may have an array of any length.

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/angular/preboot/blob/master/CONTRIBUTING.md#commit-message-format
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What modules are related to this pull-request

• server side
• client side
• inline
• build process
• docs
• tests

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  remove unused proxy imports from some test files
  A TypeScript typings fix.

• What is the current behavior? (You can also link to an open issue here)
  In the EventSelector interface, only arrays of one item are allowed for keyCodes and events.

• What is the new behavior (if this is a feature change)?
  In the EventSelector interface, arrays of varying length are allowed for keyCodes and events.

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Other information:

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[josephliccini]

@CaerusKaru thanks for merging!

When do you think this could be released to NPM?