doc: declutter generated README files

[coryan]

Part of the work for #10157

This change is 

[codecov]

Codecov Report

Base: 94.01% // Head: 94.01% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (36305bb) compared to base (8847ffa).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10562      +/-   ##
==========================================
- Coverage   94.01%   94.01%   -0.01%     
==========================================
  Files        1643     1643              
  Lines      147691   147691              
==========================================
- Hits       138858   138850       -8     
- Misses       8833     8841       +8     

Impacted Files	Coverage Δ
generator/internal/scaffold_generator.cc	85.11% <ø> (ø)
...integration_tests/schema_admin_integration_test.cc	98.88% <0.00%> (-1.12%)	⬇️
...cloud/pubsub/internal/subscription_session_test.cc	98.49% <0.00%> (-1.01%)	⬇️
...ud/spanner/integration_tests/client_stress_test.cc	84.21% <0.00%> (-0.66%)	⬇️
...le/cloud/internal/default_completion_queue_impl.cc	96.59% <0.00%> (-0.57%)	⬇️
google/cloud/storage/internal/curl_handle.cc	77.90% <0.00%> (-0.56%)	⬇️
google/cloud/storage/parallel_upload.cc	98.28% <0.00%> (-0.35%)	⬇️
google/cloud/pubsub/samples/samples.cc	87.92% <0.00%> (-0.08%)	⬇️
...le/cloud/storage/internal/curl_download_request.cc	89.63% <0.00%> (+0.33%)	⬆️
google/cloud/pubsub/subscriber_connection_test.cc	100.00% <0.00%> (+1.21%)	⬆️
... and 1 more

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