compiler: remove parentHandle from calling convention

This removes the parentHandle argument from the internal calling convention.
It was formerly used to implment coroutines.
Now that coroutines have been removed, it is no longer necessary.

compiler/calls.go

@@ -40,8 +40,7 @@ func (b *builder) createRuntimeCall(fnName string, args []llvm.Value, name strin
 	if llvmFn.IsNil() {
 		panic("trying to call non-existent function: " + fn.RelString(nil))
 	}
-	args = append(args, llvm.Undef(b.i8ptrType))            // unused context parameter
-	args = append(args, llvm.ConstPointerNull(b.i8ptrType)) // coroutine handle
+	args = append(args, llvm.Undef(b.i8ptrType)) // unused context parameter
 	return b.createCall(llvmFn, args, name)
 }