Unitary fixes (#598)

* Eliminate unneeded back-pointer to project from non-wave Tracks...

... now that DirManager is gone

* Remove unused declarations

* SampleData::mProject was not used

* Correct ProjectFileIO::GetLibraryError

* Remove unnecessary #include directives

src/Track.cpp

@@ -46,9 +46,8 @@ and TimeTrack.
 #pragma warning( disable : 4786 )
 #endif
 
-Track::Track(AudacityProject *project)
-:  vrulerSize(36,0),
-   mProject(project)
+Track::Track()
+:  vrulerSize(36,0)
 {
    mSelected  = false;
    mLinked    = false;
@@ -76,8 +75,6 @@ void Track::Init(const Track &orig)
    mDefaultName = orig.mDefaultName;
    mName = orig.mName;
 
-   mProject = orig.mProject;
-
    mSelected = orig.mSelected;
    mLinked = orig.mLinked;
    mChannel = orig.mChannel;