Replace tuple-based function definition examples with simpler types

[fredemmott]

Please complete the information below:

Where is the problem?

The examples that use tuples

What is the problem?

The syntax for tuples isn't the most readable, and adds extra parens to a situation that already has them.

The code itself is fine, but given the focus us on showing how to declare functions, it would be more readable if simpler types were used for all examples.

• • • eg "It doesn't explain that widgets are singletons" - - -

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Please don't change anything below this point.

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• Build ID: HHVM=HHVM-4.15.0:HSL=v4.7.0:2019-07-31T15:43:43+0000:982a9335b437e2a9b53d8bbdf6c9d78c5609b75b
• Page requested: /hack/functions/defining-a-function
• Page requested at: Wed, 31 Jul 2019 22:00:00 +0000
• Controller: GuidePageController