Remove un-needed "il1g" variable from ZM schemes.

[nusbaume]

Currently the zm_conv_convtran_run and zm_conv_momtran_run schemes have an "il1g" input variable which has a standard name of index_of_first_column_of_gathered_deep_convection_arrays.

However, in CAM and CAM-SIMA this variable appears to be hardcoded to one. Thus it would likely clean-up the code if this variable was removed from the relevant subroutine arguments and instead just made a local variable (or all of the relevant uses of the variable were simply replaced with 1).

Note that once this issue has been resolved the "il1g" variable can also be removed from the CAM-SIMA registry as well.

[swrneale]

In fact in some of the other convection routines there is no version of il1g passed at all and they just pass il2g (cldprp). I wonder what it would take to get rid of gathering altogether. I seem to remember @Katetc did this for microphysics a ways back.