Remove "fuzzy comparison" logic in qsort comparison function for

choose_bitmap_and().  It was way too fuzzy --- per comment, it was meant to be
1% relative difference, but was actually coded as 0.01 absolute difference,
thus causing selectivities of say 0.001 and 0.000000000001 to be treated as
equal.  I believe this thinko explains Maxim Boguk's recent complaint.  While
we could change it to a relative test coded like compare_fuzzy_path_costs(),
there's a bigger problem here, which is that any fuzziness at all renders the
comparison function non-transitive, which could confuse qsort() to the point
of delivering completely wrong results.  So forget the whole thing and just
do an exact comparison.