core, core/vm, core/state: remove unused functions

core/vm/errors.go

@@ -25,20 +25,3 @@ import (
 
 var OutOfGasError = errors.New("Out of gas")
 var DepthError = fmt.Errorf("Max call depth exceeded (%d)", params.CallCreateDepth)
-
-type StackError struct {
-	req, has int
-}
-
-func StackErr(req, has int) StackError {
-	return StackError{req, has}
-}
-
-func (self StackError) Error() string {
-	return fmt.Sprintf("stack error! require %v, have %v", self.req, self.has)
-}
-
-func IsStackErr(err error) bool {
-	_, ok := err.(StackError)
-	return ok
-}