Remove dead declarations from VTTCue and LoadableTextTrack headers

https://bugs.webkit.org/show_bug.cgi?id=318301
rdar://181098694

Reviewed by Simon Fraser.

Remove three declarations that have no definition and no callers.

* html/track/VTTCue.h:
- Remove unused m_cue member; VTTCueBox forwards its cue to the base
TextTrackCueBox and reads it back via getCue().
- Remove undefined parseSettings() declaration.
* html/track/LoadableTextTrack.h:
Remove undefined loadTimerFired() declaration.

Canonical link: https://commits.webkit.org/316315@main

Author: Ahmad-S792

Source/WebCore/html/track/LoadableTextTrack.h

@@ -58,8 +58,6 @@ class LoadableTextTrack final : public TextTrack, private TextTrackLoaderClient
     AtomString id() const final;
     bool isDefault() const final;
 
-    void loadTimerFired();
-
 #if !RELEASE_LOG_DISABLED
     ASCIILiteral logClassName() const override { return "LoadableTextTrack"_s; }
 #endif

Source/WebCore/html/track/VTTCue.h

@@ -103,9 +103,6 @@ class VTTCueBox : public TextTrackCueBox {
     VTTCueBox(Document&, VTTCue&);
 
     RenderPtr<RenderElement> createElementRenderer(Style::ComputedStyle&&, const RenderTreePosition&) final;
-
-private:
-    WeakPtr<VTTCue> m_cue;
 };
 
 // ----------------------------
@@ -239,8 +236,6 @@ class VTTCue
 
     void createWebVTTNodeTree();
 
-    void parseSettings(const String&);
-
     void determineTextDirection();
     void calculateDisplayParameters();
     void calculateDisplayParametersWithRegion();