Remove unsafe from time refcount rules #453

rules/time/tgt_refcount.rs:170:unsafe fn f9() -> nix::time::ClockId {
rules/time/tgt_refcount.rs:174:unsafe fn f10() -> nix::time::ClockId {
rules/time/tgt_refcount.rs:179:unsafe fn f11() -> nix::time::ClockId {