Simplify by removing class HitTestResult...

... Because all hit tests returned all fields blank, or else, returned a
UIHandle object whose Preview method gives the rest of the information; so
the other fields were redundant.

src/TimeTrack.h

@@ -51,7 +51,7 @@ class TimeTrack final : public Track {
    void Silence(double t0, double t1) override;
    void InsertSilence(double t, double len) override;
 
-   HitTestResult DetailedHitTest
+   UIHandlePtr DetailedHitTest
       (const TrackPanelMouseState &state,
        const AudacityProject *pProject, int currentTool, bool bMultiTool)
       override;