/**

  Remove const and eq items. Return new item, or NULL if no condition

  cond_value is set to according:

  COND_OK    query is possible (field = constant)

  COND_TRUE  always true ( 1 = 1 )

  COND_FALSE always false ( 1 = 2 )

  SYNPOSIS

    remove_eq_conds()

    thd THD environment

    cond                        the condition to handle

    cond_value                  the resulting value of the condition

  NOTES

    calls the inner_remove_eq_conds to check all the tree reqursively

  RETURN

    *COND with the simplified condition

*/