Remove several unneeded glut dependencies. Note, this doesn't signal an

immediate end to glut, only that I'm going through and cleaning up (and
taking inventory of the actual glut dependencies in case I want to investigate
SDL.)

src/Cockpit/cockpit.cxx

@@ -29,7 +29,7 @@
 #  include <windows.h>
 #endif
 
-#include GLUT_H
+#include <GL/gl.h>
 
 #include <stdlib.h>
 #include <stdio.h>

src/Cockpit/panel.hxx

@@ -36,7 +36,7 @@
 #  include <windows.h>
 #endif
 
-#include GLUT_H
+#include <GL/gl.h>
 
 #include <plib/ssg.h>
 

src/GUI/gui_funcs.cxx

@@ -40,7 +40,7 @@
 #  include <windows.h>
 #endif
 
-#include GLUT_H
+#include <GL/gl.h>
 
 #if defined(FX) && defined(XMESA)
 #  include <GL/xmesa.h>

src/Main/fg_init.cxx

@@ -31,12 +31,6 @@
 #  include <math.h>
 #endif
 
-#ifdef HAVE_WINDOWS_H
-#  include <windows.h>
-#endif
-
-#include GLUT_H
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>             // strcmp()

src/Time/light.cxx

@@ -30,7 +30,7 @@
 #  include <windows.h>
 #endif
 
-#include GLUT_H
+#include <GL/gl.h>
 
 #include <simgear/compiler.h>