Adjust TransfoParam_GR5H (production store)

The transformation given for GR5H (coming from Andrea Ficchi's files) is different from other models regarding the production store. ParamOut[, 1] <- exp(1.5 * ParamIn[, 1]) vs ParamOut[, 1] <- exp(ParamIn[, 1]) and ParamOut[, 1] <- log(ParamIn[, 1])/1.5 vs ParamOut[, 1] <- log(ParamIn[, 1]).

The 1.5 factor seems unnecessary as it provokes irrealistically high X1 values. We should try to remove it and check the impact on GR5H on our 240 catchments hourly dataset.

Issue made following a remark from @paul.astagneau