more dupe word typos

compiler/rustc_infer/src/infer/mod.rs

@@ -1150,8 +1150,8 @@ impl<'tcx> InferCtxt<'tcx> {
     /// Return the universe that the region `r` was created in.  For
     /// most regions (e.g., `'static`, named regions from the user,
     /// etc) this is the root universe U0. For inference variables or
-    /// placeholders, however, it will return the universe which which
-    /// they are associated.
+    /// placeholders, however, it will return the universe which they
+    /// are associated.
     pub fn universe_of_region(&self, r: ty::Region<'tcx>) -> ty::UniverseIndex {
         self.inner.borrow_mut().unwrap_region_constraints().universe(r)
     }