DiseasystoreGoogleCovid19: remove redundant date column

[RasmusSkytte]

In DiseasystoreGoogleCovid19, the translation from Google metrics to feature store keeps the date column.
However, this information is used to define the valid_from/until columns and are afterwards redundant.
Keeping the date column is more confusing that removing it, since it presents itself just as stratifications/observables does.

Removing the column will increase readability of the outputs and not cause loss of functionality

[RasmusSkytte]

The github action for R-CMD-Check is failing on macOS. Seems to be related to this vroom issue

[RasmusSkytte]

Since workaround introduced in PR #48 , the github actions work again