vm: fix string duplication
vm: fix string duplication

gometalinter says:

vm/vm.go:295:1:warning: fuzzerPreemptedStr is unused (deadcode)

google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller