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/event_loop.rs

@@ -38,9 +38,4 @@ impl EventLoop {
     pub fn send(&self, msg: ScriptThreadMessage) -> Result<(), Error> {
         self.script_chan.send(msg)
     }
-
-    /// The underlying channel to the script thread.
-    pub fn sender(&self) -> IpcSender<ScriptThreadMessage> {
-        self.script_chan.clone()
-    }
 }