rustdoc: Reduce internal function visibility.

As suggested in
1862fcb1df (r1211200570).

src/librustdoc/html/format.rs

@@ -1459,7 +1459,7 @@ fn inner_full_print(
         Ok(())
     }
 
-    pub(crate) fn print_output<'a, 'tcx: 'a>(
+    fn print_output<'a, 'tcx: 'a>(
         &'a self,
         cx: &'a Context<'tcx>,
     ) -> impl fmt::Display + 'a + Captures<'tcx> {