Changes

Remove upsilon 0 and 1 if branches (#1365)

* Removed unnecessary upsilon_precip_frac_rat == 0 or 1 checks

The read in parameter upsilon_precip_frac_rat is set in .in files.
upsilon_precip_frac_rat describes the precipitation ratio between the first and second
PDF component.
The edge cases, all perticipitation in one PDF (upsilon=0 or 1) had their
own if branches. These edge case branches are not strictly necessary as upsilon
should never be set to 0 or 1 and we can live with a tiny precipitation fraction of
precip_frac_tol in such a case.
Furthermore a logic error was present which would never execute the if branch for the upsilon=0 case anyway.
Per default upsilon is not set to 0 and afaik is not tested in the jenkins tests.
However if upsilon is read in as 0 or 1 this commit would be technically BIT_CHANGING.

A mirrored code removal in clubb-jax was also done.

* changed comment about role of upsilon a bit