destutil: remove duplicate check and leave it to merge.update() The check is done in merge.update() already and the next few patches will add more checks there. Some of the additional checks will need information about the merge that will not be available in destutil. Since commands.postincoming() catches UpdateAbort(), we need to change merge.update() to raise that more specific exception. This goes directly again 45b86dbabbda (destupdate: move the check related to the "clean" logic in the function, 2015-10-05), but it will simplify the next few patches, and we can always move it out again (preferably move, not copy) after if we still think it's better that way.