code: public void removeIndexedColumn(ByteBuffer column)
      {
          SecondaryIndex index = indexesByColumn.remove(column);
  
          if (index == null)
              return;
  
          // Remove this column from from row level index map as well as all indexes set
          if (index instanceof PerRowSecondaryIndex)
          {
              index.removeColumnDef(column);
  
              // If no columns left remove from row level lookup as well as all indexes set
              if (index.getColumnDefs().isEmpty())
              {
                  allIndexes.remove(index);
                  rowLevelIndexMap.remove(index.getClass());
              }
          }
          else
          {
              allIndexes.remove(index);
          }
  
          index.removeIndex(column);
          SystemKeyspace.setIndexRemoved(baseCfs.metadata.ksName, index.getNameForSystemKeyspace(column));
      }
docs: Removes a existing index
  @param column the indexed column to remove