Texas case data time series file recreated

[CSSEGISandData]

Further to #5213, we have recreated the Texas county-level time series files to match those published by the Texas Department of Health Service. Doing so allows us to remove the artificial state level spike and the volatility in the county-level data. We have received confirmation from the state their confirmed time series and probable time series are organized by date of report so they are suitable for our repository.

Within the 2020 file of the Texas state time series files, there were included 47,583 confirmed cases and 5,707 probable cases with an 'unknown date' entry. As recommended by the state, we have assigned these cases to December 31, 2020.

Please let us know any questions.