pgsql: Remove table AM callback scan_bitmap_next_block

Remove table AM callback scan_bitmap_next_block

After pushing the bitmap iterator into table-AM specific code (as part
of making bitmap heap scan use the read stream API in 2b73a8cd33b7),
scan_bitmap_next_block() no longer returns the current block number.
Since scan_bitmap_next_block() isn't returning any relevant information
to bitmap table scan code, it makes more sense to get rid of it.

Now, bitmap table scan code only calls table_scan_bitmap_next_tuple(),
and the heap AM implementation of scan_bitmap_next_block() is a local
helper in heapam_handler.c.

Reviewed-by: Tomas Vondra <tomas(at)vondra(dot)me>
Discussion: https://postgr.es/m/flat/CAAKRu_ZwCwWFeL_H3ia26bP2e7HiKLWt0ZmGXPVwPO6uXq0vaA%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c3953226a07527a1e2f7f410b83e1a7021f42888

Modified Files
--------------
src/backend/access/heap/heapam_handler.c | 372 ++++++++++++++++--------------
src/backend/access/table/tableamapi.c | 3 -
src/backend/executor/nodeBitmapHeapscan.c | 73 ++----
src/backend/optimizer/util/plancat.c | 2 +-
src/include/access/tableam.h | 90 ++------
5 files changed, 244 insertions(+), 296 deletions(-)