edit_line bundle manage_variable_values_ini should not edit fields

The manage_variable_values_ini edit_line bundle in lib/files.cf now tries to edit fields in the particular INI file section. But it also deletes all lines from the section and then inserts new lines from based on the given data. So trying to edit the fields doesn't make sense, especially because the evaluation deletes all the lines in the section before trying to edit the fields. But in general, it should just delete everything in the section and insert the new lines. There is set_variable_values_ini for editing values in an INI section.