Title pretty much covers it, I am looking Nat building a shelter to keep all of my water treatment devices out of the elements that I have outside. This will include water filters, water softener, however I do have a pressure vacuum breaker valve that upon inspection I noticed will need to be replaced.

Our home sprinkler is on our well water line so it is completely separated from the city water that feeds our house. This city line only provides water to the house and nothing else. Do I actually need to replace this with another valve or can I remove it entirely and just bury the line back underground?

I wouldn't put one in especially since the sprinkler system is not involved. You might ask a local plumber about code compliance though.