SQL: deletion of "sql_defer_foreign_keys" session setting

[TarantoolBot]

Product: Tarantool
Since: 2.11
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/_session_settings/
https://www.tarantool.io/en/doc/latest/reference/reference_sql/sql_statements_and_clauses/
SME: @ ImeevMA

• Mark settiing as deprecated
• Fix list formatting in the root document

Details

Because "constraint check time" is no longer supported by foreign keys,
the session setting "sql_defer_foreign_keys" has no meaning and is
discarded.
Requested by @ImeevMA in tarantool/tarantool@14618c4.