MDEV-36839: Revert MDEV-7409

MDEV-6247 added PROCESSLIST states for when a Replication
SQL thread processes Row events, including a WSRep variant
that dynamically includes the Galera Sequence Number.
MDEV-7409 further expanded on it by adding the table name to the states.

However, PROCESSLIST __cannot__ support generated states.
Because it loads the state texts asynchronously,
only permanently static strings are safe.
Even thread-local memory can become invalid when the thread terminates,
which can happen in the middle of generating a PROCESSLIST.

To prioritize memory safety, this commit reverts both variants to
static strings as the non-WSRep variant was before MDEV-7409.
* __Fully__ revert MDEV-7409 (d9898c9a71)
* Remove the WSRep override from MDEV-6247
  * Remove `THD::wsrep_info` and its compiler
    flag `WSREP_PROC_INFO` as they are now unused

This commit also includes small optimizations
from MDEV-36839’s previous draft, #4133.

Reviewed-by: Brandon Nesterenko <brandon.nesterenko@mariadb.com>

sql/sql_class.h

@@ -5553,7 +5553,6 @@ public:
   uint32                    wsrep_rand;
   rpl_group_info            *wsrep_rgi;
   bool                      wsrep_converted_lock_session;
-  char                      wsrep_info[128]; /* string for dynamic proc info */
   ulong                     wsrep_retry_counter; // of autocommit
   bool                      wsrep_PA_safe;
   char*                     wsrep_retry_query;