score:6
You haven't 'Submitted' your DS-160 to the consulate. Fundamentally, you submit it to the consulate when you appear there for your interview (technically now days you generally just submit a reference page, but they don't consider it as being submitted until that point).
So no, you will have no issues with what you've done, and there is no need to delete the original application for London. The original DS-160 you filled will never be acted upon, and will probably eventually be silently deleted.