Chore: Remove unused GetFocusTopLevelBrowsingContext from EmbedderToConstellationMessage (#37716)

This is a legacy message used only by WebDriver to focus the webview,
when session just created. Right now this is just dead_code which is not
detected by Lint.

Testing: No behaviour change.

Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>

components/constellation/tracing.rs

@@ -50,9 +50,6 @@ mod from_compositor {
         fn log_target(&self) -> &'static str {
             match self {
                 Self::Exit => target!("Exit"),
-                Self::GetFocusTopLevelBrowsingContext(..) => {
-                    target!("GetFocusTopLevelBrowsingContext")
-                },
                 Self::IsReadyToSaveImage(..) => target!("IsReadyToSaveImage"),
                 Self::AllowNavigationResponse(..) => target!("AllowNavigationResponse"),
                 Self::LoadUrl(..) => target!("LoadUrl"),