rustdoc: remove redundant item kind class from `.item-decl > pre`

This class originated in the very first commit of `rustdoc_ng`, and was used
to add a color border around the item decl based on its kind.

https://github.com/rust-lang/rust/blob/4fd061c426902b0904c65e64a3780b21f9ab3afb/src/rustdoc_ng/html/static/main.css#L102-L106

The item decl no longer has a border, and there aren't any
kind-specific styles in modern rustdoc's rendering of this UI item.

Most of this commit is updating test cases so that they use `item-decl` to
find the `<pre>` tag instead of relying on the fact that the class name
had `rust {kind}` in it while other `<pre>` tags only had class `rust`.

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/rustdoc/legacy-const-generic.rs b/tests/rustdoc/legacy-const-generic.rs
index 46a50e2fc30..14533624e44 100644
--- a/tests/rustdoc/legacy-const-generic.rs
+++ b/tests/rustdoc/legacy-const-generic.rs
@@ -2,14 +2,14 @@
 #![feature(rustc_attrs)]
 
 // @has 'foo/fn.foo.html'
-// @has - '//*[@class="rust fn"]' 'fn foo(x: usize, const Y: usize, z: usize) -> [usize; 3]'
+// @has - '//div[@class="item-decl"]/pre[@class="rust"]' 'fn foo(x: usize, const Y: usize, z: usize) -> [usize; 3]'
 #[rustc_legacy_const_generics(1)]
 pub fn foo<const Y: usize>(x: usize, z: usize) -> [usize; 3] {
     [x, Y, z]
 }
 
 // @has 'foo/fn.bar.html'
-// @has - '//*[@class="rust fn"]' 'fn bar(x: usize, const Y: usize, const Z: usize) -> [usize; 3]'
+// @has - '//div[@class="item-decl"]/pre[@class="rust"]' 'fn bar(x: usize, const Y: usize, const Z: usize) -> [usize; 3]'
 #[rustc_legacy_const_generics(1, 2)]
 pub fn bar<const Y: usize, const Z: usize>(x: usize) -> [usize; 3] {
     [x, Y, z]