Filing down calluses
Today I had to file down the callus on my first finger because the callus grew into the shape of the string indentation on my finger. Recently, it had gotten so deep that the string would buzz under my finger unless I pressed too hard, the filing fixed it. Is this a normal thing to do, or is it a symptom of me pressing the string too hard?
You may be pressing too hard and you may be using strings that are too thick. If you are playing in high positions your strings may be too high above the fingerboard. They could be too high at the nut and/or at the bridge. Near the nut the string height should be about the thickness of a normal business card.
Nathan Cole made a great video about left hand finger pressure. I think you're pressing too hard.
Can't see what you're doing and/or not doing, but it does sound like a case of pressing too hard. Whatever it is, you shouldn't have actual calluses. Some toughening or leathering is common, though, and shouldn't cause any problems -- in fact, I find it desirable.
Just keep a piece of 100-grit garnet sandpaper in your case and use that just a little before you practice.