Thanks for your reply! I went through and looked again in Components > Calendar Administrator [actually, it's "Calendar Administator"

] and there is no option to delete any calendars, only to add them. I've added my calendar to the list (ID 4), but can't get rid of the default ones that were already there (IDs 1, 2 and 3), and there is no need for either them or the dropdown to choose which calendar, since there will only be one.
I've gone through and commented/labelled the CSS where I can find out what it's doing, but don't think I need a whole skin (call me lazy!).
Seems like I should be able to prevent stuff from being inserted, somehow... Will keep looking