Cleanups

- Remove not used thd_rpl_is_parallel()
- Remove not used mysql_notify_thread_having_shared_lock()
- Remove not needed LOCK_thread_count from MYSQL_BIN_LOG::reset_logs()
  - LOCK_thread_count is not protecting against rollback, so this
    code and comment is not needed
- Remove mutex_locks in slave.cc that are not needed.
  Added THD::assert_not_linked() to ensure that it was safe to remove
- Fixed not repeatable test load_data_stmt_view
- Updated binlog_killed to test removal of mutex
  (thanks to Andrei Elkin for test)
- More code comments

include/mysql/plugin_encryption.h.pp

@@ -518,7 +518,6 @@ void **thd_ha_data(const void* thd, const struct handlerton *hton);
 void thd_storage_lock_wait(void* thd, long long value);
 int thd_tx_isolation(const void* thd);
 int thd_tx_is_read_only(const void* thd);
-int thd_rpl_is_parallel(const void* thd);
 int mysql_tmpfile(const char *prefix);
 unsigned long thd_get_thread_id(const void* thd);
 void thd_get_xid(const void* thd, MYSQL_XID *xid);