Remove parameter from call to btr_search_validate().
buf0buf.c:
  Initialize member "index" of buf_block_t.
buf0buf.h:
  Add member "index" to buf_block_t.
btr0sea.h:
  Remove parameter of btr_search_validate()
btr0sea.c:
  Make use of the added member "index" of buf_block_t.