[docs] fix typo in AutoencoderOobleck docs (#13642)

[ivnvalex]

What does this PR do?

Fixes #13642
Typo in AutoencoderOobleck docs: duplicated OobleckDecoderOutput descriptions

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@stevhliu or @sayakpaul please check guys! Thank you!

[stevhliu]

thanks!

[HuggingFaceDocBuilderDev]

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