Correct the error checking in subset_data

[ekluzek]

Some error checking was turned off in subset_data in #2155. Rather than turning it off the error checking should be fixed so it works correctly and asks for the right thing.

For example here in #2155:

            # -- check dom_pft vs MAX_pft
            if self.num_pft - 1 < max_dom_pft < NUM_PFT:
                logger.info(
                    "WARNING, you trying to run with generic crops (16 PFT surface dataset)"
                )
                # raise argparse.ArgumentTypeError(err_msg)

And

                logger.info(
                    "WARNING, you are subsetting using mixed land units that have both natural pfts and crop cfts. Check that your surface dataset looks correct."
                )
                raise argparse.ArgumentTypeError(err_msg)