Remove unused variables from ptend structure

### Issue Type

Code Clean-up

### Issue Description

The following variables are set but never used in the ptend structure:

- hflux_srf
- hflux_top
- taux_srf
- taux_top
- tauy_srf
- tauy_top

A search through a very old cam tag (cam3_2_47) revealed that even back in that tag, these variables were set and never used.

@brian-eaton - Do you happen to know why these variables were set and never used, or more importantly, if there is any reason not to remove them now?

### Will this change answers?

No

### Will you be implementing this yourself?

Any CAM SE can do this