Clean-up tracer_data: increment_string use in incr_filename

### Issue Type

Code Clean-up

### Issue Description

During review of #441, @fvitt originally wrote:
> I don't think we actually use this feature in cam. This was left over from the old MOZART chemical transport model. Not sure that increment_string needs to migrated to CAM-SIMA.

For the `increment_string` function added to support this block of code:
https://github.com/ESCOMP/CAM-SIMA/blob/8dcd0e8ca7ba348dcb32e9a48b3605d3dc13b578/src/utils/tracer_data.F90#L990-L1005

That appears to be unused in CAM-SIMA (and CAM).

This feature could be removed, and if `increment_string` has no other purpose now or in the future, it can also be removed from CAM-SIMA entirely.

### Will this change answers?

No

### Will you be implementing this yourself?

Yes