make love build on OS X again - there's no need to include gl.h directly, GLee.h does that for us in a cross-platform way

src/modules/graphics/opengl/ParticleSystem.cpp

@@ -22,7 +22,7 @@
 
 #include <common/math.h>
 
-#include <GL/gl.h>
+#include "GLee.h"
 #include <cmath>
 #include <cstdlib>
 

src/modules/graphics/opengl/SpriteBatch.h

@@ -36,7 +36,6 @@
 
 // OpenGL
 #include "GLee.h"
-#include <GL/gl.h>
 
 namespace love
 {

src/modules/graphics/opengl/VertexBuffer.h

@@ -27,7 +27,6 @@
 
 // OpenGL
 #include "GLee.h"
-#include <GL/gl.h>
 
 namespace love
 {