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

sql/sql_class.cc

@@ -4775,13 +4775,6 @@ extern "C" int thd_slave_thread(const MYSQL_THD thd)
   return(thd->slave_thread);
 }
 
-/* Returns true for a worker thread in parallel replication. */
-extern "C" int thd_rpl_is_parallel(const MYSQL_THD thd)
-{
-  return thd->rgi_slave && thd->rgi_slave->is_parallel_exec;
-}
-
-
 /* Returns high resolution timestamp for the start
   of the current query. */
 extern "C" unsigned long long thd_start_utime(const MYSQL_THD thd)