chore: simplify sample rows key callable chain

[igorbernstein2]

Previously there were 3 chain creators:

1. createSampleRowKeysBaseCallable
2. createSampleRowKeysWithRequestCallable
3. createSampleRowKeysCallable

The primary reason for this is that SampleRowKeysWithRequest was introduced after createSampleRowKeysCallable because it supports authorized views.

This pr simplifies the logic by moving everything into createSampleRowKeysWithRequestCallable and makes createSampleRowKeysCallable be a tiny shim to convert a String tableId into a SampleRowKeysRequest

Change-Id: I8f3f33936211bccc71fb0345c5d87fd9f85b2146

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Fixes #<issue_number_goes_here> ☕️

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