Cleanup reassigning friction_type 4 to 2 for structures

[martijn-siemerink]

threedigrid-builder/threedigrid_builder/interface/db.py

Line 539 in 43f878c

arr["friction_type"][arr["friction_type"] == 4] = 2

For all structures the reassigning of friction_type 4 to 2 needs to be removed (this is very old legacy). We now have a meaningful friction_type 4 (manning_conveyance), so conversion will lead to problems.

Note: Probably only the testbank will have friction_types 4 that do not mean manning_conveyance. Please check!