In particular:

* @@debug
  deprecated since 5.5.37
* sr_YU locale
  deprecated since 10.0.11
* "engine_condition_pushdown" in the @@optimizer_switch
  deprecated since 10.1.1
* @@date_format, @@datetime_format, @@time_format, @@max_tmp_tables
  deprecated since  10.1.2
* @@wsrep_causal_reads
  deprecated since 10.1.3
* "parser" in mroonga table comment
  deprecated since 10.2.11