Fix errors introduced during rebasing

Author: shinglyu

vm/src/obj/objlist.rs

@@ -10,7 +10,6 @@ use super::objsequence::{
 };
 use super::objstr;
 use super::objtype;
-use num_bigint::ToBigInt;
 use num_traits::ToPrimitive;
 
 // set_item:

vm/src/vm.rs

@@ -121,11 +121,6 @@ impl VirtualMachine {
         self.new_exception(os_error, msg)
     }
 
-    pub fn new_overflow_error(&mut self, msg: String) -> PyObjectRef {
-        let overflow_error = self.ctx.exceptions.overflow_error.clone();
-        self.new_exception(overflow_error, msg)
-    }
-
     /// Create a new python ValueError object. Useful for raising errors from
     /// python functions implemented in rust.
     pub fn new_value_error(&mut self, msg: String) -> PyObjectRef {