Update existing tests

Author: veera-sivarajan

tests/ui/cast/cast-to-slice.stderr

@@ -1,7 +1,7 @@
 error[E0620]: cast to unsized type: `&[u8]` as `[char]`
   --> $DIR/cast-to-slice.rs:2:5
    |
-LL |     "example".as_bytes() as [char]; 
+LL |     "example".as_bytes() as [char];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^------
    |                             |
    |                             help: try casting to a reference instead: `&[char]`

tests/ui/error-codes/E0620.stderr

@@ -2,13 +2,9 @@ error[E0620]: cast to unsized type: `&[usize; 2]` as `[usize]`
   --> $DIR/E0620.rs:2:16
    |
 LL |     let _foo = &[1_usize, 2] as [usize];
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: consider using an implicit coercion to `&[usize]` instead
-  --> $DIR/E0620.rs:2:16
-   |
-LL |     let _foo = &[1_usize, 2] as [usize];
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                ^^^^^^^^^^^^^^^^^-------
+   |                                 |
+   |                                 help: try casting to a reference instead: `&[usize]`
 
 error: aborting due to 1 previous error
 

tests/ui/issues/issue-17441.stderr

@@ -2,13 +2,9 @@ error[E0620]: cast to unsized type: `&[usize; 2]` as `[usize]`
   --> $DIR/issue-17441.rs:2:16
    |
 LL |     let _foo = &[1_usize, 2] as [usize];
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-help: consider using an implicit coercion to `&[usize]` instead
-  --> $DIR/issue-17441.rs:2:16
-   |
-LL |     let _foo = &[1_usize, 2] as [usize];
-   |                ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                ^^^^^^^^^^^^^^^^^-------
+   |                                 |
+   |                                 help: try casting to a reference instead: `&[usize]`
 
 error[E0620]: cast to unsized type: `Box<usize>` as `dyn Debug`
   --> $DIR/issue-17441.rs:5:16