The aggregate_results function was aggregating losses across components
for each asset. This is unnecessary since it is already done by Pelicun
earlier in the workflow. Aggregation can be more complex than simply
summing up losses for each component. So, it is more appropriate to use
the DL_summary_stats file directly and rely on Pelicun to take care of
the appropriate aggregation.

This commit modifies the code to drop the old functionality and utilize
DL_summary_stats.

In another, minor update, it also fixes a bug in naming.
R2Dres_mean_RepairCost is used when results are scaled with replacement
costs. When such scaling is not performed, the
R2Dres_mean_RepairCost_{cost_unit} naming is used. Consequently, when
loss ratios are returned by a method and we have replacement cost
available, rWHALE will return both the loss ratios and the absolute
losses.