Remove wording about requiring a space and colon

[laurelmay]

This is somewhat confusing language that doesn't seem to be present for the other top-level keys within the template. In YAML, it would even be odd to include such a space and it isn't necessary in JSON.

Issue #, if available:

Description of changes:

Removed a section of a sentence to make the documentation of the Outputs section match that for other sections such as Mappings and Resources.

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