A haunted dead giant is following me around Skyrim

Dead bodies appearing when you load an area is a fairly common bug in Skyrim, I've had it a lot with dragons (although it may just be confirmation bias in that I notice those corpses the easiest).

To fix this specific case, you can open the console (` or ~) and click on the dead giant. Make double sure that it says you've selected the giant and not something else, then type disable or markfordelete and press enter. This should remove the giant.