[refactor-contentdiv4] evolve: remove unnecessary code since it's been covered already

We don't need this logic any more since the case of "two divergent csets where one is the parent of other" has been handled correctly by the logic present in method _prepcontentdivresolution()

This is how things works in method _prepcontentdivresolution() for our case i.e "content-divergence with parent-child relation":

cset_b (content-divergent) | cset_a (content-divergent) | ~

Acc. to revision selection criteria: "divergent" = min_revision(cset_a, cset_b) So always "divergent" will be cset_a and "other" will be "cset_b" and resolution parent will be the successor of parent of cset_a. Both the csets will be merged and resolution cset will be based on correct revision. The result could be wrong only in the case when "divergent" is cset_b which is not possible acc. to the current logic.