MDEV-21688 Assertion or ER_WARN_DATA_OUT_OF_RANGE upon ALTER on previously versioned table

Earlier skip of history row. Cleanup of dead code for VTMD.

mysql-test/suite/versioning/r/alter.result

@@ -684,3 +684,12 @@ add column c int without system versioning,
 change column c c int,
 change column b b int without system versioning;
 drop table t;
+#
+# MDEV-21688 Assertion or ER_WARN_DATA_OUT_OF_RANGE upon ALTER on previously versioned table
+#
+create or replace table t1 (a int) with system versioning;
+insert into t1 values (128);
+delete from t1;
+set statement system_versioning_alter_history=keep for
+alter table t1 drop system versioning, modify column a tinyint;
+drop table t1;

mysql-test/suite/versioning/t/alter.test

@@ -580,3 +580,15 @@ alter table t
   change column b b int without system versioning;
 
 drop table t;
+
+--echo #
+--echo # MDEV-21688 Assertion or ER_WARN_DATA_OUT_OF_RANGE upon ALTER on previously versioned table
+--echo #
+create or replace table t1 (a int) with system versioning;
+insert into t1 values (128);
+delete from t1;
+set statement system_versioning_alter_history=keep for
+alter table t1 drop system versioning, modify column a tinyint;
+
+# cleanup
+drop table t1;

sql/sql_table.cc

@@ -10379,7 +10379,6 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
   bool make_versioned= !from->versioned() && to->versioned();
   bool make_unversioned= from->versioned() && !to->versioned();
   bool keep_versioned= from->versioned() && to->versioned();
-  bool drop_history= false; // XXX
   Field *to_row_start= NULL, *to_row_end= NULL, *from_row_end= NULL;
   MYSQL_TIME query_start;
   DBUG_ENTER("copy_data_between_tables");
@@ -10507,10 +10506,6 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
   {
     from_row_end= from->vers_end_field();
   }
-  else if (keep_versioned && drop_history)
-  {
-    from_row_end= from->vers_end_field();
-  }
 
   THD_STAGE_INFO(thd, stage_copy_to_tmp_table);
   /* Tell handler that we have values for all columns in the to table */
@@ -10542,6 +10537,13 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
       error= 1;
       break;
     }
+
+    if (make_unversioned)
+    {
+      if (!from_row_end->is_max())
+        continue; // Drop history rows.
+    }
+
     if (unlikely(++thd->progress.counter >= time_to_report_progress))
     {
       time_to_report_progress+= MY_HOW_OFTEN_TO_WRITE/10;
@@ -10561,20 +10563,12 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
       copy_ptr->do_copy(copy_ptr);
     }
 
-    if (drop_history && from_row_end && !from_row_end->is_max())
-      continue;
-
     if (make_versioned)
     {
       to_row_start->set_notnull();
       to_row_start->store_time(&query_start);
       to_row_end->set_max();
     }
-    else if (make_unversioned)
-    {
-      if (!from_row_end->is_max())
-        continue; // Drop history rows.
-    }
 
     prev_insert_id= to->file->next_insert_id;
     if (to->default_field)