Remove martian chance from salesman spawn

[Mouse]

I for one think if Martians are gonna be resprited they ought to also be redesigned, since the actual design of them is ripped directly from Metal Slug. We can be more original than just taking a different game's martians !

Which are themselves taken from an adaptation of War of the Worlds, as I recall.  Not necessarily directly, the octopus/jellyfish martian is the standard depiction in Japanese media.