Drop explicit linking of GL libraries.

The pkg-config of Qt5OpenGL should refer to them.

Author: niemeyer

gl/gl.go

@@ -3,8 +3,6 @@ package gl
 // #cgo CXXFLAGS: -std=c++0x -pedantic-errors -Wall -fno-strict-aliasing 
 // #cgo CPPFLAGS: -DGL_GLEXT_PROTOTYPES -DGL_GLEXT_LEGACY
 // #cgo LDFLAGS: -lstdc++
-// #cgo !darwin LDFLAGS: -lGL
-// #cgo  darwin LDFLAGS: -framework OpenGL
 // #cgo pkg-config: Qt5Core Qt5Widgets Qt5Quick Qt5OpenGL
 //
 // #include "gl.h"