GLContext: Fix framebuffer deletion to GPUContext

This has more meaning as it's the base class who holds the pointer.

# Conflicts:
#	source/blender/gpu/opengl/gl_context.cc

source/blender/gpu/intern/gpu_context.cc

@@ -71,6 +71,10 @@ GPUContext::~GPUContext()
 {
   GPU_matrix_state_discard(matrix_state);
   delete state_manager;
+  delete front_left;
+  delete back_left;
+  delete front_right;
+  delete back_right;
 }
 
 bool GPUContext::is_active_on_thread(void)

source/blender/gpu/opengl/gl_context.cc

@@ -101,11 +101,6 @@ GLContext::~GLContext()
   }
   glDeleteVertexArrays(1, &default_vao_);
   glDeleteBuffers(1, &default_attr_vbo_);
-
-  delete front_left;
-  delete back_left;
-  delete front_right;
-  delete back_right;
 }
 
 /** \} */