Cycles: Fix missing mesh flags update when tweaking shaders

This is a bit weak, but better than tagging whole mesh manager for update.

Maybe we'll solve such dual-look up in the future.

This commit finally solves T48963: Noise when changing Diffuse node to Emission node

intern/cycles/render/mesh.h

@@ -122,7 +122,6 @@ public:
 	array<bool> forms_quad; /* used to tell if triangle is part of a quad patch */
 
 	bool has_volume;  /* Set in the device_update_flags(). */
-	bool has_mis_emission;  /* Set in the device_update_flags(). */
 	bool has_surface_bssrdf;  /* Set in the device_update_flags(). */
 
 	array<float3> curve_keys;