avast I believe would normally caution on files detected in the system folders, but that is no guarantee and I would never recommend deletion even if this were a certainty, 'first do no harm' don't delete, you have zero options left, send to the chest.
Lets deal with the best option, 'Move to the chest,' this is a protected area where an infected file can't be accessed nor can do any harm. From here if needs be the copy can be restored to the original location, extracted (copied to a temp location) or sent to avast for further analysis.
Move is also a move and rename option they are sent to the C:\Program Files\Alwil Software\Avast4\DATA\moved folder, this not a protected area and .vir is tagged on to the end of, e.g. infectedfile.exe.vir. This also means you have a copy that because it has been moved and renamed it shouldn't be active, but allows for similar actions as move to the chest.