Stop supporting the additional *trunc.log files that were
introduced via MySQL 5.7 to MariaDB Server 10.2 and 10.3.

DB_TABLESPACE_TRUNCATED: Remove.

purge_sys.truncate: A new structure to track undo tablespace
file truncation.

srv_start(): Remove the call to buf_pool_invalidate(). It is
no longer necessary, given that we no longer access things in
ways that violate the ARIES protocol. This call was originally
added for innodb_file_format, and it may later have been necessary
for the proper function of the MySQL 5.7 TRUNCATE recovery, which
we are now removing.

trx_purge_cleanse_purge_queue(): Take the undo tablespace as a
parameter.

trx_purge_truncate_history(): Rewrite everything mostly in a
single function, replacing references to undo::Truncate.

recv_apply_hashed_log_recs(): If any redo log is to be applied,
and if the log_sys.log.subformat indicates that separately
logged truncate may have been used, refuse to proceed except if
innodb_force_recovery is set. We will still refuse crash-upgrade
if TRUNCATE TABLE was logged. Undo tablespace truncation would
only be logged in undo*trunc.log files, which we are no longer
checking for.