MDEV-21210: main.uniques_crash-7912 tries to allocate 1TB of memory

Remove the offending test case. This sort of error is hard to test in
all possible corner cases and thus makes the test less valuable. The
overflow error will be covered by warnings generated by the compiler,
which is much more reliable in the general case.

mysql-test/r/uniques_crash-7912.result

-call mtr.add_suppression("Out of memory");
-set sql_mode="";
-drop table if exists t1,t2;
-create table `t1` (`a` datetime not null) engine=InnoDB;
-create table `t2` (`a` int not null) engine=innodb;
-replace into t1 values (),();
-insert into t2 values(0);
-set session sort_buffer_size = 1024*1024*1024*1024;
-delete d2 from t2 as d1, t1 as d2 where d1.a <=> d2.a;
-drop table t2;
-drop table t1;

mysql-test/t/uniques_crash-7912.test

-#
-# MDEV-7912
-#
-# multitable delete with wrongly set sort_buffer_size crashes in merge_buffers
-
---source include/have_innodb.inc
---source include/have_debug.inc
---source include/windows.inc
-
-call mtr.add_suppression("Out of memory");
-
-set sql_mode="";
---disable_warnings
-drop table if exists t1,t2;
-create table `t1` (`a` datetime not null) engine=InnoDB;
-create table `t2` (`a` int not null) engine=innodb;
-replace into t1 values (),();
-insert into t2 values(0);
-set session sort_buffer_size = 1024*1024*1024*1024;
-#Either fail with EE_OUTOFMEMORY, or succeed
---error 0 , 5
-delete d2 from t2 as d1, t1 as d2 where d1.a <=> d2.a;
---enable_warnings
-
-drop table t2;
-drop table t1;