compositor: Remove the script channel from the compositor (#36089)

This is a clean up after #36062 and #35985. It removes the script
channel for each pipeline from the compositor. Now all messages are sent
via the `Constellation` first, which will allow breaking the dependency
on script in the compositor.

In addition, scroll states are actually sent via the `Constellation`,
which was an oversight from #36062. Finally, a typo in a method name is
fixed.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/constellation/pipeline.rs

@@ -422,7 +422,6 @@ impl Pipeline {
         CompositionPipeline {
             id: self.id,
             webview_id: self.webview_id,
-            script_chan: self.event_loop.sender(),
         }
     }