You cannot remove content yourself, nor any one person, therefore it's immutable. It's of no consequence that a consensus among the witnesses could alter the database as not one person could alter it. The consensus isn't controlled by any one individual either, in any way. So what if there's a hypothetical situation where consensus can alter the data, obviously even in such an event the mere gathering of consensus will allow the old one to be stored and archived, not that the consensus of the witnesses will change the fact that not you or anyone else can change the data, therefore it's most immutable. It falls under the paradoxical aspect in such a case, obviously we call it immutable but in another hypothetical situation where all the machines of all the witnesses get infected and compromised the data then is infected and compromised, does that not make it immutable, no, it doesn't. Simply because a far off scenario exists and can be implemented is not going to make the data any more prone to being altered.
The question was "Can you remove content from the blockchain?"
The only answer there is to that is an unequivocal no, because if you can then it's imperative you show exactly how you can do it, theory or practice.
You've added a restriction that it must be changeable by an individual. No such restriction should be expected when calling something immutable. Immutable as a term on it's own in binary, it is changeable or not. I also specifically stated that it relies on the definition of the blockchain being the currently accepted consensus. That does not include backups and rogue chains.
In the fully possible scenario I described it is clearly not immutable. Not everything is a paradox and our universe has binaries.
The probability of it happening has no bearing on whether it is immutable. The ability to change it is baked into it's design. Just like ethereum is not immutable they changed the blockchain.