Remove ancient register allocation (#3401)

cranelift/codegen/src/inst_predicates.rs

@@ -78,10 +78,3 @@ pub fn is_constant_64bit(func: &Function, inst: Inst) -> Option<u64> {
         _ => None,
     }
 }
-
-/// Is the given instruction a safepoint (i.e., potentially causes a GC, depending on the
-/// embedding, and so requires reftyped values to be enumerated with a stack map)?
-pub fn is_safepoint(func: &Function, inst: Inst) -> bool {
-    let op = func.dfg[inst].opcode();
-    op.is_resumable_trap() || op.is_call()
-}