Remove unused tropopause methods in tropopause_find

@nusbaume wrote during the code review (https://github.com/ESCOMP/atmospheric_physics/pull/112) for `tropopause_find`:
> I know we are generally trying to avoid clean-up for now, but I think it would be good make an issue reminding us to eventually remove all tropopause algorithm options that aren't being used currently in tropopause_find_run, as my suspicion is that some of these options aren't used at all anymore.

This is an issue as a reminder to remove these unused methods. All combinations used in current CAM have been included in `tropopause_find`; other methods remain as method subroutines but are inaccessible in CCPP.

```
integer, parameter :: TROP_ALG_NONE = 1 ! Don't evaluate
integer, parameter :: TROP_ALG_ANALYTIC = 2 ! Analytic Expression
integer, parameter :: TROP_ALG_CLIMATE = 3 ! Climatology
integer, parameter :: TROP_ALG_STOBIE = 4 ! Stobie Algorithm
integer, parameter :: TROP_ALG_TWMO = 5 ! WMO Definition, Reichler et al. [2003]
integer, parameter :: TROP_ALG_WMO = 6 ! WMO Definition
integer, parameter :: TROP_ALG_HYBSTOB = 7 ! Hybrid Stobie Algorithm
integer, parameter :: TROP_ALG_CPP = 8 ! Cold Point Parabolic
integer, parameter :: TROP_ALG_CHEMTROP = 9 ! Chemical tropopause
```