Remove store_temperature option

[danieljprice]

the store_temperature option is now redundant (temperature is always stored) and can be removed from the code.

Since the equation of state also now returns the temperature for all choices of ieos, we should also remove all superfluous "get_temperature" routines.

Suggest that temperature should only be written to the dump file if a non-ideal equation of state is used, to avoid wasting disk space

Originally posted by @danieljprice in https://github.com/danieljprice/phantom/pull/86#issuecomment-724400949