docs(samples): add delete dataset and contents

[pmakani]

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[codecov]

Codecov Report

Merging #629 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #629 +/- ## ============================================ + Coverage 81.45% 81.49% +0.04%  - Complexity 1225 1226 +1  ============================================ Files 77 77 Lines 6200 6220 +20 Branches 677 691 +14 ============================================ + Hits 5050 5069 +19  - Misses 791 792 +1  Partials 359 359 

Impacted Files	Coverage Δ	Complexity Δ
...e/cloud/bigquery/testing/RemoteBigQueryHelper.java	61.40% <0.00%> (-0.42%)	6.00% <0.00%> (ø%)
...ain/java/com/google/cloud/bigquery/Clustering.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...ain/java/com/google/cloud/bigquery/PolicyTags.java	100.00% <0.00%> (ø)	6.00% <0.00%> (ø%)
...java/com/google/cloud/bigquery/BigtableColumn.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...java/com/google/cloud/bigquery/TimelineSample.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...om/google/cloud/bigquery/ModelTableDefinition.java	100.00% <0.00%> (ø)	4.00% <0.00%> (ø%)
...om/google/cloud/bigquery/LoadJobConfiguration.java	93.20% <0.00%> (+0.02%)	56.00% <0.00%> (ø%)
...ogle/cloud/bigquery/WriteChannelConfiguration.java	86.81% <0.00%> (+0.06%)	46.00% <0.00%> (ø%)
...google/cloud/bigquery/StandardTableDefinition.java	93.33% <0.00%> (+0.09%)	16.00% <0.00%> (ø%)
...om/google/cloud/bigquery/BigtableColumnFamily.java	96.00% <0.00%> (+0.16%)	5.00% <0.00%> (ø%)
... and 8 more

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