Update clippy ui test.

The reason we do not trigger these lints anymore is that clippy sets the mir-opt-level to 0, and the recent changes subtly changed how the const propagator works.

tests/ui/indexing_slicing_index.stderr

@@ -1,23 +1,3 @@
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:11:5
-   |
-LL |     x[4]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^ index out of bounds: the len is 4 but the index is 4
-   |
-   = note: `#[deny(unconditional_panic)]` on by default
-
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:12:5
-   |
-LL |     x[1 << 3]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^^^^^^ index out of bounds: the len is 4 but the index is 8
-
-error: this operation will panic at runtime
-  --> $DIR/indexing_slicing_index.rs:27:5
-   |
-LL |     x[N]; // Ok, let rustc's `const_err` lint handle `usize` indexing on arrays.
-   |     ^^^^ index out of bounds: the len is 4 but the index is 15
-
 error: indexing may panic.
   --> $DIR/indexing_slicing_index.rs:10:5
    |
@@ -75,5 +55,5 @@ LL |     v[M];
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
-error: aborting due to 10 previous errors
+error: aborting due to 7 previous errors