So the UW-Stout administration has been asked about this patently ridiculous decision, and a couple of days ago its spokesperson came out with this brilliant retort, which has convinced me that the original poster was too dangerous to allow college students to ever see:

"The word 'kill' is in there," UW-Stout spokesman Doug Mell said. "There's no question about that."
It wouldn't be so sad if that was not the only apparent defense. And then he tried to defend the removal of the second poster:

Mell says that "[t]he second poster was taken down because obviously it depicts violence."
Apparently all action movie posters are SERIOUS THREATS that must be stopped.

As to why the university continues to refuse to protect an obvious First Amendment right:

Mell explains that "[o]ur action has to be viewed in the context of post-Virginia Tech and post-Northern Illinois."
Apparently Virginia Tech and Northern Illinois is the college equivalent of "9/11," used to justify any abject stupidity. Anyway, here's a FIRE blog entry with a bunch of links to online reactions to this story, for those interested.