Auto merge of #23007 - BartGitHub:remove-pipeline-visibility-checks, r=jdm

Remove pipeline visibility checks

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This includes the following changes/clean-ups:

- Remove ```is_visible``` field from ```Pipeline``` struct
- Remove ```SetVisible``` script message, and related message sending/handling.

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<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #22986

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- [x] These changes do not require tests because the issue description states having a passing build is enough for a pull request.

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components/script_traits/script_msg.rs

@@ -175,8 +175,6 @@ pub enum ScriptMsg {
     /// Notification that this iframe should be removed.
     /// Returns a list of pipelines which were closed.
     RemoveIFrame(BrowsingContextId, IpcSender<Vec<PipelineId>>),
-    /// Change pipeline visibility
-    SetVisible(bool),
     /// Notifies constellation that an iframe's visibility has been changed.
     VisibilityChangeComplete(bool),
     /// A load has been requested in an IFrame.
@@ -243,7 +241,6 @@ impl fmt::Debug for ScriptMsg {
             ReplaceHistoryState(..) => "ReplaceHistoryState",
             JointSessionHistoryLength(..) => "JointSessionHistoryLength",
             RemoveIFrame(..) => "RemoveIFrame",
-            SetVisible(..) => "SetVisible",
             VisibilityChangeComplete(..) => "VisibilityChangeComplete",
             ScriptLoadedURLInIFrame(..) => "ScriptLoadedURLInIFrame",
             ScriptNewIFrame(..) => "ScriptNewIFrame",