Ethernet port plastic plug blocking port access on server
Those are PadJack Locks.:
They can't be removed without breaking them. They don't come from Dell that way, someone else installed them. They're meant to be difficult to removed, and tamper-evident.
If I remember correctly the back end has a "top" and "bottom" that you pry up/down (apart) until it snaps. I could be wrong, it's been a while since I've seen them, so don't quote me on that...
I have removed one of these using a drill and a few drill bits. Use around a 1/8" bit to drill a pilot hole, then a 1/4" to make it larger, then maybe a 5/16". Once it's large enough, you can just pry out the pieces with some needle-nose pliers. It's not for the faint of heart, but it did work. If I had to do it again, I'd probably try the paperclip method mentioned in the comments first.