docs(events): Remove await from eventEmitter.emit example

[wilfreud]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs
• Other... Please describe:

What is the current behavior?

Documentation is indicating a synchronous method call with unnecessary await keyword.

Issue Number: N/A

What is the new behavior?

Documentation is a little more "accurate", as a synchronous function does not need await keyword during call.

Does this PR introduce a breaking change?

• Yes
• No