fix pose code snippet

[gabrielsanchez]

First issue: mp_holistic is not defined in this snippet. It was replaced by mp_pose.
Second issue: model_complexity=2 is available for MediaPipe Holistic but not for MediaPipe Pose.

The snippet will work with the changes that I made.

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[gabrielsanchez]

@googlebot I signed it!

[jiuqiant]

Thanks for reporting this. Fixed in our internal code base upstream, and will be pushed to GitHub in the next release.

[jiuqiant]

Fixed in 6abec12.