upkeep: only use join_ald_scenario when necessary

[jdhoffa]

join_ald_scenario is necessary to call prior to target_*. However, it pollutes summarize_* with unnecessary scenario columns, requiring either:

1. the user to manually group the remaining columns
2. the developer (me) to select the crucial columns and call distinct() prior to summarizing

1 puts a lot of onus on the user to know what they are doing (which i am skeptical of). 2 is a bit of a strict enforcement on our part... I propose we remove join_ald_scenario from the summarize_* helpfiles and regression tests, and assume the input has only lbk and ald columns, and suggest that the user use the ... argument to add further groups, in the case of inputs with multiple scenarios etc.

[jdhoffa]

Relates to #468