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

[parthea]

Towards googleapis/google-cloud-python#10908.

[snippet-bot]

Here is the summary of changes.

You are about to delete 2 region tags.

• samples/generated_samples/lifesciences_v2beta_generated_workflows_service_v2_beta_run_pipeline_async.py:26, tag lifesciences_v2beta_generated_WorkflowsServiceV2Beta_RunPipeline_async
• samples/generated_samples/lifesciences_v2beta_generated_workflows_service_v2_beta_run_pipeline_sync.py:26, tag lifesciences_v2beta_generated_WorkflowsServiceV2Beta_RunPipeline_sync

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