MDEV-30256 Wrong result (missing rows) upon join with empty table

The problem was an assignment in test_quick_select() that flagged empty
tables with "Impossible where". This test was however wrong as it
didn't work correctly for left join.

Removed the test, but added checking of empty tables in DELETE and UPDATE
to get similar EXPLAIN as before.

The new tests is a bit more strict (better) than before as it catches all
cases of empty tables in single table DELETE/UPDATE.

mysql-test/main/filesort_debug.test

@@ -86,6 +86,8 @@ CREATE TABLE t1 (
   primary key (pk)
 );
 
+insert into t1 (pk) values (1),(2),(3);
+
 CALL mtr.add_suppression("Out of sort memory");
 
 --error ER_OUT_OF_SORTMEMORY