Satisfy SGI CC: don't give default param value in implementation.

src/Plot.cc

@@ -13,7 +13,7 @@ int Plot_inpick( Fl_Plot *plot ) { return plot->inpick(); }
 
 void Plot_setpick( Fl_Plot *, void (*pickcb)(Fl_Plot *, int hits, int ents, GLuint *buf) );
 
-Fl_Plot::Fl_Plot(int x, int y, int w, int h, const char *label = 0)
+Fl_Plot::Fl_Plot(int x, int y, int w, int h, const char *label)
 		: Fl_Gl_Window(x,y,w,h,label) {
   init();
   end();