Remove workarounds for the BQ Storage API issue with small result sets

[plamut]

Context: #55 (comment)

The BigQuery Storage API has an issue with fetching small result sets, thus the BigQuery library implements a fallback to tabledata.list API. Since the fix for that issue on the backend will be rolled out soon, the fallback will not be necessary anymore and should be removed.

[emkornfield]

@plamut FWIW, the fix has finished rolling out on the backend.

[plamut]

@emkornfield Oh, that's great! Thanks for the heads-up!