Remove unnecessary ticks (#664)

Commands in the strikethrough-style ended up with ticks around their strikethrough characters.
We can safely remove these ticks, as the command names are already modified and surrounded by ticks.

src/framework/standard/help_commands.rs

@@ -999,7 +999,7 @@ fn flatten_group_to_plain_string(
         );
     }
 
-    let joined_commands = format!("`{}`", group.command_names.join("`, `"));
+    let joined_commands = format!("{}", group.command_names.join(", "));
 
     let _ = write!(group_text, "{}", joined_commands);