Remove unused feature from a miri test

tests/ui/consts/miri_unleashed/ptr_arith.rs

@@ -1,5 +1,4 @@
 // compile-flags: -Zunleash-the-miri-inside-of-you
-#![feature(core_intrinsics)]
 
 // During CTFE, we prevent pointer-to-int casts.
 // Pointer comparisons are prevented in the trait system.

tests/ui/consts/miri_unleashed/ptr_arith.stderr

@@ -1,11 +1,11 @@
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ptr_arith.rs:8:13
+  --> $DIR/ptr_arith.rs:7:13
    |
 LL |     let x = &0 as *const _ as usize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^ exposing pointers is not possible at compile-time
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/ptr_arith.rs:16:14
+  --> $DIR/ptr_arith.rs:15:14
    |
 LL |     let _v = x + 0;
    |              ^ unable to turn pointer into integer
@@ -16,7 +16,7 @@ LL |     let _v = x + 0;
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/ptr_arith.rs:8:13
+  --> $DIR/ptr_arith.rs:7:13
    |
 LL |     let x = &0 as *const _ as usize;
    |             ^^^^^^^^^^^^^^^^^^^^^^^