cleanup: remove redundant vers_field->set_notnull();

as these fields are always declared NOT NULL anyway

sql/log_event.cc

@@ -13571,9 +13571,6 @@ int Rows_log_event::find_row(rpl_group_info *rgi)
     // check whether master table is unversioned
     if (row_end->val_int() == 0)
     {
-      // row_start initialized with NULL when came from plain table.
-      // Set it notnull() because record_compare() count NULLs.
-      table->vers_start_field()->set_notnull();
       bitmap_set_bit(table->write_set, row_end->field_index);
       // Plain source table may have a PRIMARY KEY. And row_end is always
       // a part of PRIMARY KEY. Set it to max value for engine to find it in

sql/sql_insert.cc

@@ -1933,7 +1933,6 @@ int write_record(THD *thd, TABLE *table,COPY_INFO *info)
           if (table->versioned(VERS_TRX_ID))
           {
             bitmap_set_bit(table->write_set, table->vers_start_field()->field_index);
-            table->vers_start_field()->set_notnull();
             table->vers_start_field()->store(0, false);
           }
           if ((error=table->file->ha_update_row(table->record[1],

sql/table.cc

@@ -7764,14 +7764,12 @@ void TABLE::vers_update_fields()
   {
     if (!vers_write)
       return;
-    vers_start_field()->set_notnull();
     if (vers_start_field()->store_timestamp(in_use->system_time,
                                             in_use->system_time_sec_part))
       DBUG_ASSERT(0);
   }
   else
   {
-    vers_start_field()->set_notnull();
     if (!vers_write)
       return;
   }
@@ -7782,7 +7780,6 @@ void TABLE::vers_update_fields()
 
 void TABLE::vers_update_end()
 {
-  vers_end_field()->set_notnull();
   if (vers_end_field()->store_timestamp(in_use->system_time,
                                         in_use->system_time_sec_part))
     DBUG_ASSERT(0);