Make using a 16-PFT fire emissions dataset in a 78-PFT run trigger an error

[ekluzek]

In ctsm5.3.0 we update to using a 78 PFT fire emissions dataset. But, we also made sure that you could use the previous 16 PFT one. Going forward it might be better to trigger use of 16 PFT as an error.

As @samsrabin says here...

Well, my original concern is still there—if ( size(factors) > npfts ) will never be true here as long as if ( npfts < maxveg ) in fire_emis_factors_init() triggers an error.

• Do we want the user to be able to run with a too-short emissions file or not? If yes, delete that error check (and rename npfts to something more descriptive, like npfts_on_emis_file). If no, delete this conditional (and the npft variable).

I say no—I don't like it when the model silently resolves what might have been a mistake on my part.

Originally posted by @samsrabin in #2500 (comment)