libobs-opengl: Store FBOs per texture instead of per device

The previous model stored a new FBO per texture width/height/format on
a array in the device struct. This allocated memory was only released
on gs_device_destroy (obs exit).

The new approach stores a FBO on gs_texture and the its info is
destroyed once the texture is deleted.

libobs-opengl/gl-texture2d.c

@@ -138,6 +138,9 @@ void gs_texture_destroy(gs_texture_t *tex)
 	if (tex->texture)
 		gl_delete_textures(1, &tex->texture);
 
+	if (tex->fbo)
+		fbo_info_destroy(tex->fbo);
+
 	bfree(tex);
 }