cleanup: clarify ha_innobase::column_bitmaps_signal()

it was created to handle the case of the concurrent
inplace add index. So it should only work in that case,
otherwise it's doing server's job (marks virtual column dependencies)
and hides server's bugs. And it was redundant.

storage/innobase/handler/ha_innodb.cc

@@ -5116,13 +5116,21 @@ ha_innobase::keys_to_use_for_scanning()
 	return(&key_map_full);
 }
 
-/** Ensure that indexed virtual columns will be computed. */
+/****************************************************************//**
+Ensure that indexed virtual columns will be computed.
+Needs to be done for indexes that are being added with inplace ALTER
+in a different thread, because from the server point of view these
+columns are not yet indexed.
+*/
 void ha_innobase::column_bitmaps_signal()
 {
   if (!table->vfield || table->current_lock != F_WRLCK)
     return;
 
   dict_index_t* clust_index= dict_table_get_first_index(m_prebuilt->table);
+  if (!clust_index->online_log)
+    return;
+
   uint num_v= 0;
   for (uint j = 0; j < table->s->virtual_fields; j++)
   {