[PATCH OBVIOUS]Remove unused structure field inv_expr

[Bin Cheng]

Hi,
This patch removed unused field inv_expr in struct cost_pair left over by 
previous refactoring.
Build on x86_64.  Applying as obvious.

Thanks,
bin
2017-05-04  Bin Cheng  <bin.ch...@arm.com>

        * tree-ssa-loop-ivopts.c (struct cost_pair): Remove field inv_expr
        which is not used any more.
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 7caa40d..adb985b 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -353,7 +353,6 @@ struct cost_pair
   tree value;          /* For final value elimination, the expression for
                           the final value of the iv.  For iv elimination,
                           the new bound to compare with.  */
-  iv_inv_expr_ent *inv_expr; /* Loop invariant expression.  */
 };
 
 /* Use.  */