The suicide scene itself was indeed deleted, but we do see Colin's body in the mid-credits scenes.
These images are from The Thing (2011), I promise.The related shots in The Thing (1982) are similar, but slightly different
The reason they cut it was related to the special effects problems that plagued the production.
When Edvard-Thing transforms, his arms fall off and become mini-Things.
The idea was that his legs also broke off and became mini-Things. Colin locks himself in the storage room, and finds that one of the mini-Things, in the form of Edvard's calf and foot, is in the room with him. You can hear the sound effect of the leg-Thing scuttling around in the clip you posted; the plan was to add the visual effects later, but that never happened.
The reasons they didn't insert the visual effect - and therefore, cut out that part of the scene:
It looked stupid. There would be a calf and foot crawling around in a menacing way, but it looked absurd instead of scary. After the director saw how ridiculous the leg-Thing looked, he decided to scrap the idea altogether.
It screwed up the pacing of the climax and drew attention away from Kate.
Personally, I think the absurdity of the leg-Thing's appearance was a much more important factor than any other considerations.
From a fan site Q&A with director Matthijs Van Heijningen Jr.:
Just to give an update on the deleted Colin scene. This is what was planned but due to money and repetitiveness of another limb scene was skipped. When Colin turns around, he sees Edvard’s leg crawling on to the ledge and transforms into a crazy entity, blocking him to escape to the autopsy lab. We never designed that creature's transformation during filming, we figured we would do that in post. We started designing it but it looked a little weird and almost comical, seeing a leg crawling up the ledge. We also skipped it because I felt that it pointed too much attention on Colin and we needed to focus on Kate and Carter searching the camp. Jonathan Walker put down a great performance but it took very long to make it believable. You are not just cutting your wrists and slicing your throat. It slowed the action down and took the story away from Kate and Carter.
From a fan site Q&A with Jonathan Lloyd Walker (the actor who played Colin):
Glad you guys liked the scene! Obviously I was acting on the day with nothing there and somehow the scene on the DVD works without the CGI creature. However, I understand why it got cut for the sake of the build toward the climax on the alien ship. Matthijs, it’s a shame some of the scenes that were shot prior to reshoots didn’t make it onto the DVD, would’ve been fun to see some of those. I think if I were isolated like Colin, amongst strangers or people I had little connection to, I would choose to get out on my own terms rather than be a victim. I see that as a stronger choice. However, Colin was a loner. I have kids. I want to believe that my will to fight to survive is increased in a situation this bizarre by my need to get home to them and keep them safe. So maybe I would have fought harder even if it was futile. I can’t really answer that definitively since people don’t know how they will react in crisis until they are in crisis.
Here's what the scene would have looked like with leg-Thing:
See the problem?
Note regarding your suggestion that without the scene, one is left to imagine that Colin was killed by the Thing:
Not so much. Remember, this is a prequel, and a prequel to a cult classic. Once Colin locked himself up alone, the bulk of the audience would have pegged him as the suicide victim from the original.
And even if his death were left unexplained, it wouldn't be unprecedented within the franchise: in the original, the deaths of Fuchs and Nauls are left a mystery, as is the fate of MacReady and Childs, as well as the question of whether either MacReady or Childs are infected.
