fix unused import

Author: RalfJung

src/librustc_codegen_ssa/mir/block.rs

@@ -2,7 +2,7 @@ use rustc::middle::lang_items;
 use rustc::ty::{self, Ty, TypeFoldable, Instance};
 use rustc::ty::layout::{self, LayoutOf, HasTyCtxt, FnTypeExt};
 use rustc::mir::{self, Place, PlaceBase, Static, StaticKind};
-use rustc::mir::interpret::{InterpError, PanicMessage};
+use rustc::mir::interpret::PanicMessage;
 use rustc_target::abi::call::{ArgType, FnType, PassMode, IgnoreMode};
 use rustc_target::spec::abi::Abi;
 use crate::base;