Drop access to native window.

The new NFD library is not using this information, and the old one was using
it only on Windows. Oh well.

Removal of this functionality also removes some build-time decisions.

server/TracySourceView.cpp

@@ -222,7 +222,7 @@ static void PrintSourceFragment( const SourceContents& src, uint32_t srcline, in
 enum { JumpSeparationBase = 6 };
 enum { JumpArrowBase = 9 };
 
-SourceView::SourceView( GetWindowCallback gwcb )
+SourceView::SourceView()
     : m_font( nullptr )
     , m_smallFont( nullptr )
     , m_symAddr( 0 )
@@ -248,7 +248,6 @@ SourceView::SourceView( GetWindowCallback gwcb )
     , m_showJumps( true )
     , m_cpuArch( CpuArchUnknown )
     , m_showLatency( false )
-    , m_gwcb( gwcb )
 {
     m_microArchOpMap.reserve( OpsNum );
     for( int i=0; i<OpsNum; i++ )