Cleanup: Remove mesh valid assertions in debug builds

These are useful for development, but when the primitive nodes
aren't actively changing, the performance cost is not worth it.

source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_circle.cc

@@ -213,8 +213,6 @@ static void node_geo_exec(GeoNodeExecParams params)
 
   Mesh *mesh = create_circle_mesh(radius, verts_num, fill);
 
-  BLI_assert(BKE_mesh_is_valid(mesh));
-
   params.set_output("Mesh", GeometrySet::create_with_mesh(mesh));
 }
 

source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_grid.cc

@@ -212,7 +212,6 @@ static void node_geo_exec(GeoNodeExecParams params)
   }
 
   Mesh *mesh = create_grid_mesh(verts_x, verts_y, size_x, size_y);
-  BLI_assert(BKE_mesh_is_valid(mesh));
   BKE_id_material_eval_ensure_default_slot(&mesh->id);
 
   params.set_output("Mesh", GeometrySet::create_with_mesh(mesh));

source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_uv_sphere.cc

@@ -287,8 +287,6 @@ static Mesh *create_uv_sphere_mesh(const float radius, const int segments, const
 
   calculate_sphere_uvs(mesh, segments, rings);
 
-  BLI_assert(BKE_mesh_is_valid(mesh));
-
   return mesh;
 }