- Description:
  - Before 10.3.8 semisync was a plugin that is built into the server with
    MDEV-13073,starting with commit cbc71485.
    There are still some usage of `rpl_semi_sync_master` in mtr.
Note:
  - To recognize the replica in the `dump_thread`, replica is creating
    local variable `rpl_semi_sync_slave` (the keyword of plugin) in
    function `request_transmit`, that is catched by primary in
    `is_semi_sync_slave()`. This is the user variable and as such not
    related to the obsolete plugin.

 - Found in `sys_vars.all_vars` and `rpl_semi_sync_wait_point` tests,
   usage of plugins `rpl_semi_sync_master`, `rpl_semi_sync_slave`.
   The former test is disabled by default (`sys_vars/disabled.def`)
   and marked as `obsolete`, however this patch will remove the queries.

- Add cosmetic fixes to semisync codebase

Reviewer: <brandon.nesterenko@mariadb.com>
Closes PR #2528, PR #2380