The following fold_* functions, as well as Lmap_bitwise.Location_map_bitwise.map2 take arguments
of type map to force their user to handle the cases Top and Bottom
explicitly.
Return the set of stmts (scope) where annot has the same value
than in stmt
and add to to_be_removed the annotations that are identical to annot
in the statements that are both the scope and that are dominated by stmt.