build: update README to indicate that source has moved and delete all files

[parthea]

Towards googleapis/google-cloud-python#10965.

[snippet-bot]

Here is the summary of changes.

You are about to delete 12 region tags.

• samples/generated_samples/videointelligence_v1_generated_video_intelligence_service_annotate_video_async.py:26, tag videointelligence_v1_generated_VideoIntelligenceService_AnnotateVideo_async
• samples/generated_samples/videointelligence_v1_generated_video_intelligence_service_annotate_video_sync.py:26, tag videointelligence_v1_generated_VideoIntelligenceService_AnnotateVideo_sync
• samples/generated_samples/videointelligence_v1beta2_generated_video_intelligence_service_annotate_video_async.py:26, tag videointelligence_v1beta2_generated_VideoIntelligenceService_AnnotateVideo_async
• samples/generated_samples/videointelligence_v1beta2_generated_video_intelligence_service_annotate_video_sync.py:26, tag videointelligence_v1beta2_generated_VideoIntelligenceService_AnnotateVideo_sync
• samples/generated_samples/videointelligence_v1p1beta1_generated_video_intelligence_service_annotate_video_async.py:26, tag videointelligence_v1p1beta1_generated_VideoIntelligenceService_AnnotateVideo_async
• samples/generated_samples/videointelligence_v1p1beta1_generated_video_intelligence_service_annotate_video_sync.py:26, tag videointelligence_v1p1beta1_generated_VideoIntelligenceService_AnnotateVideo_sync
• samples/generated_samples/videointelligence_v1p2beta1_generated_video_intelligence_service_annotate_video_async.py:26, tag videointelligence_v1p2beta1_generated_VideoIntelligenceService_AnnotateVideo_async
• samples/generated_samples/videointelligence_v1p2beta1_generated_video_intelligence_service_annotate_video_sync.py:26, tag videointelligence_v1p2beta1_generated_VideoIntelligenceService_AnnotateVideo_sync
• samples/generated_samples/videointelligence_v1p3beta1_generated_streaming_video_intelligence_service_streaming_annotate_video_async.py:26, tag videointelligence_v1p3beta1_generated_StreamingVideoIntelligenceService_StreamingAnnotateVideo_async
• samples/generated_samples/videointelligence_v1p3beta1_generated_streaming_video_intelligence_service_streaming_annotate_video_sync.py:26, tag videointelligence_v1p3beta1_generated_StreamingVideoIntelligenceService_StreamingAnnotateVideo_sync
• samples/generated_samples/videointelligence_v1p3beta1_generated_video_intelligence_service_annotate_video_async.py:26, tag videointelligence_v1p3beta1_generated_VideoIntelligenceService_AnnotateVideo_async
• samples/generated_samples/videointelligence_v1p3beta1_generated_video_intelligence_service_annotate_video_sync.py:26, tag videointelligence_v1p3beta1_generated_VideoIntelligenceService_AnnotateVideo_sync

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