Fix T79007: Smooth brushes crasing in dyntopo

The custom smooth functions for bmesh and meshes where removed and
replaced by a generic smooth function using the sculpt API, which needs
to initialize the bmesh indices in order to be used

Reviewed By: sergey

Maniphest Tasks: T79007

Differential Revision: https://developer.blender.org/D8333

source/blender/editors/sculpt_paint/sculpt_smooth.c

@@ -415,6 +415,8 @@ void SCULPT_smooth(Sculpt *sd,
     return;
   }
 
+  SCULPT_vertex_random_access_init(ss);
+
   for (iteration = 0; iteration <= count; iteration++) {
     const float strength = (iteration != count) ? 1.0f : last;