Revert "vim-patch:8.1.0822: peeking and flushing output slows down execution"

This reverts commit 0519a75f6e.

src/nvim/getchar.c

@@ -2490,10 +2490,8 @@ int inchar(
     }
 
     // Always flush the output characters when getting input characters
-    // from the user and not just peeking.
-    if (wait_time == -1L || wait_time > 10L) {
-      ui_flush();
-    }
+    // from the user.
+    ui_flush();
 
     // Fill up to a third of the buffer, because each character may be
     // tripled below.