Remove unused tropopause methods in tropopause_find

[jimmielin]

@nusbaume wrote during the code review (#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