epoll: remove unnecessary instructions

A couple of instructions were left over from an earlier rebase
it would seem. They don't impact the logic but the ready_list type
is about to change in the next commit.

Rather than modify one of these lines in the commit that changes
ready_list, only to have these lines removed later on, remove them now.
They don't impact the tests results.

Author: FrankReh

src/tools/miri/src/shims/unix/linux/epoll.rs

@@ -207,9 +207,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             );
         }
 
-        let mut epoll_instance = Epoll::default();
-        epoll_instance.ready_list = Rc::new(RefCell::new(BTreeMap::new()));
-
         let fd = this.machine.fds.insert_new(Epoll::default());
         Ok(Scalar::from_i32(fd))
     }