Remove Print::Output

Now that `Printer` doesn't have subprinters anymore, the output of a
printing operation is always the same.

compiler/rustc_const_eval/src/util/type_name.rs

@@ -140,7 +140,7 @@ impl<'tcx> PrettyPrinter<'tcx> for AbsolutePathPrinter<'tcx> {
     }
     fn comma_sep<T>(mut self, mut elems: impl Iterator<Item = T>) -> Result<Self, Self::Error>
     where
-        T: Print<'tcx, Self, Output = Self, Error = Self::Error>,
+        T: Print<'tcx, Self, Error = Self::Error>,
     {
         if let Some(first) = elems.next() {
             self = first.print(self)?;