i doubt they'd remove it for security reasons - as you say, there's nothing secret about what this plane is doing here. more that they'd remove it for the same reasons they remove clouds or any other in-air objects that obscure the thing they're actually trying to take photos of.

the plane isn't part of the map, so it shouldn't be on the map. even if it's not obscuring anything, they use satellite photos to generate building outlines, and this isn't a building. given how many planes there are flying all the time, and how infrequently you see them on google maps, they must make an effort to publish satellite imagery that doensn't have planes in it.