[doc] Move class definition to the correct section
minor #935 [doc] Move class definition to the correct section (GromNaN)

This PR was merged into the 1.2.x-dev branch.

Discussion
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[doc] Move class definition to the correct section

In the doc on the `SectionServiceProvider`, the section about validating arrays don't need classes. Their definition is more relevant it the section about validating objects.

Commits
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6d03fe4 [doc] Move class definition to the correct section