fix branch on uninit in spatial_editor_plugin

Moved the initialisation of origin_enabled up a bit, to be inited before
it's accessed in _init_grid. A step towards cleaner valgrind output and
removes an opportunity for a random occurance of the origin/grid
z-fighting issue.

Also removed unused variable last_grid_snap to avoid later confusion.

editor/plugins/spatial_editor_plugin.h

@@ -510,7 +510,6 @@ private:
 	RID grid[3];
 	RID grid_instance[3];
 	bool grid_visible[3]; //currently visible
-	float last_grid_snap;
 	bool grid_enable[3]; //should be always visible if true
 	bool grid_enabled;