Rollup merge of #58894 - GuillaumeGomez:invalid-lifetime-bounds, r=estebank

Fix invalid bounds string generation in rustdoc

Fixes #58737.

Very weird and I'm not sure this is the best fix around. However, trying to fix it beforehand seems overly complicated compared to the gain (in `clean`, it wouldn't change anything since we **have to** return something so that wouldn't work, and in `hir`, I'm afraid I'd break something else for very little gain).

Also, I wasn't able to make a small code to reproduce the issue. The only way to test is to document `crossbeam` directly and check the `Scope` struct...

r? @QuietMisdreavus

src/test/rustdoc/useless_lifetime_bound.rs

@@ -0,0 +1,13 @@
+use std::marker::PhantomData;
+
+// @has useless_lifetime_bound/struct.Scope.html
+// @!has - '//*[@class="rust struct"]' "'env: 'env"
+pub struct Scope<'env> {
+    _marker: PhantomData<&'env mut &'env ()>,
+}
+
+// @has useless_lifetime_bound/struct.Scope.html
+// @!has - '//*[@class="rust struct"]' "T: 'a + 'a"
+pub struct SomeStruct<'a, T: 'a> {
+    _marker: PhantomData<&'a T>,
+}