Avoid duplication of variables

[SarahAlidoost]

As a part of fixing #97, I noticed some variables are duplicated just with a different name. For example in STEMMUS_SCOPE.m:

% Convert unit to Centimeter-Gram-Second system
HR_a = 0.01 .* (ForcingData.RH_msr);
U = 100 .* (ForcingData.WS_msr);
TopPg = 100 .* (ForcingData.Pg_msr);

First the unit conversion should be moved to where it is used. Second, it can be refactored as:

% Convert unit to Centimeter-Gram-Second system
ForcingData.RH_msr = 0.01 .* (ForcingData.RH_msr);

relates to #141

[yijianzeng]

Thanks a lot Sarah, this is also linked to the unit of input data. Perhaps, shall we avoid hard-coding such unit conversion factor? Just a quick thought.