sym_tab_free_private(): Do not call dict_table_close(), but
simply invoke dict_table_t::release(), which we can do without
locking the whole dictionary cache. (Note: On user tables it
may still be necessary to invoke dict_table_close(), so that
InnoDB persistent statistics will be deinitialized as expected.)

fts_check_corrupt(), row_fts_merge_insert(): Invoke
aux_table->release() to simplify the code. This is never a user table.

fts_que_graph_free(), fts_que_graph_free_check_lock(): Replaced with
que_graph_free().

Reviewed by: Thirunarayanan Balathandayuthapani