Backup/restore: remove legacy binlog-server based PITR code

[shlomi-noach]

Years ago, a third party entity introduced point-in-time recovery based on mysql-ripple. That entity no longer uses said approach; the vitess team does not support it; in the years since we've not become aware of anyone else using it; mysql-ripple is archived.

We have termed this as "legacy" since v17: https://vitess.io/docs/archive/17.0/reference/features/recovery/

Vitess offers incremental backups and point in time recoveries based on binary logs and the standard mysqlbinlog binary.

We propose to completely remove the codebase that supports the binlog server approach.

Related:

• RFC: incremental backup and point-in-time recovery #11227
• Point in time recovery (PITR) #4886
• Point in time recovery (part 1) #5160
• RFC: Point in time recovery (PITR) Part 2 #6267
• Implemented PITR-2 #6408