Update mercure.rst: Deleting forgotten(?) sentence

Page: https://symfony.com/doc/5.x/mercure.html#debugging

Config instructions were added at #12598 and later removed at #15924

But I can't get the profiler to work. On which page am I supposed to open it? I guess on the one containing the JavaScript? (i.e. same page as I see the EventStrems in Chrome DevTools)?
What do I have to do to get this to work?
On the profiler page, the "Mercure" entry is always greyed out.

Author: ThomasLandauer

mercure.rst

@@ -684,8 +684,6 @@ Debugging
 
     The WebProfiler panel was introduced in MercureBundle 0.2.
 
-Enable the panel in your configuration, as follows:
-
 MercureBundle is shipped with a debug panel. Install the Debug pack to
 enable it::