By that logic, wouldn't they have to remove Steel?
(well ok that's even worse logic but I still feel that's sort of silly)
I am going to comment on this with a caveat - I am not fully informed of the situation here.
But, I believe that before the author of the map went to work for Splash Damage, valve bought the rights to Steel. For all intents and purposes, Steel is Valve's, and they can keep it.
However, now that he went to work for Splash Damage, freight is technically the property of Splash Damage. Why? The company pays to train the author how to map, and an argument could be made that this knowledge went into the creation of freight, and Splash Damage can claim the rights to it.
(ain't copyright law a b****?)
Also, I've said this before, congrats on the map, and for what its worth, I've played it in 6v6, 12v12 and 16v16 and I've had a blast with it.