post-migration docs cleanup

[chalmerlowe]

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Summary of the issue

As part of the migration to the google-cloud-python mono-repo, several internal cross-references in the docs no longer worked (largely due to inline links to deleted samples).

A deeper look should be given to the deleted files OR references to see whether there is value in reconstituting those links.

google-cloud-bigquery:
See commit: a62aa46

API client name and version

No response

Reproduction steps: code

file: main.py

   def reproduce():
    # complete code here

Reproduction steps: supporting files

file: mydata.csv

alpha,1,3
beta,2,5

Reproduction steps: actual results

file: output.txtmydata.csv

Calculated: foo

Reproduction steps: expected results

file: output.txtmydata.csv

Calculated: bar

OS & version + platform

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Python environment

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Python dependencies

No response

Additional context

No response