Fix warning in UNetMotionModel

[DN6]

What does this PR do?

The UNetMotionModel is initialized from the pretrained UNet2DConditionModel config. Many of the parameters supported by the 2D UNet are not present in the UNetMotionModel which can result in fairly long warning messages that are not really actionable, since these parameters cannot be removed from the original 2D UNet's config.

This PR filters out the unnecessary parameters from the config dict before creating the UNetMotionModel so that these warnings are not raised.

Fixes # (issue)

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[yiyixuxu]

thanks!