Get rid of unneeded aliases field

src/librustdoc/formats/cache.rs

@@ -120,10 +120,6 @@ crate struct Cache {
     // when gathering trait documentation on a type, hold impls here while
     // folding and add them to the cache later on if we find the trait.
     orphan_trait_impls: Vec<(DefId, FxHashSet<DefId>, Impl)>,
-
-    /// Aliases added through `#[doc(alias = "...")]`. Since a few items can have the same alias,
-    /// we need the alias element to have an array of items.
-    crate aliases: BTreeMap<String, Vec<usize>>,
 }
 
 /// This struct is used to wrap the `cache` and `tcx` in order to run `DocFolder`.