innodb_lru_flush_size configuration is no longer used

MDEV-33613 eliminated page flush from LRU by session thread ( ) when no free pages are found in LRU. The configuration innodb_lru_flush_size used to control the number of pages to be flushed also got unused.

buf_block_t *buf_LRU_get_free_block(bool have_mutex)

{

...

if (!buf_flush_LRU(innodb_lru_flush_size, true)) {

                MONITOR_INC(MONITOR_LRU_SINGLE_FLUSH_FAILURE_COUNT);

                ++flush_failures;

}

Based on discussion with marko, we can deprecate the parameter and eventually remove.