[rtve] Fix RTVEInfantil

[bictorman]

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• Bug fix
• Improvement
• New extractor
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Description of your pull request and other information

RTVEInfantil stopped working with ERROR: Unable to extract internal video ID, as vidplayer_id disappeared but video_id works just fine. This PR removes the unnecessary failing step.

[felisucoibi]

+1

[bdovaz]

Any news on this? I'm having this problem.