failing unit test: vtqueryserver on debian10/mariadb 10.3

[morgo]

I am getting a consistently failing unit test when running the tests in the included MariaDB 10.3 in Debian 10:

ok  	vitess.io/vitess/go/vt/vtgate/vtgateconn	0.003s
--- FAIL: TestPassthroughDMLs (0.02s)
    endtoend_test.go:228: expected error but got: <nil>
--- FAIL: TestTransactions (0.00s)
    endtoend_test.go:258: error: Duplicate entry '1' for key 'PRIMARY' (errno 1062) (sqlstate 23000) (CallerID: userData1): Sql: "insert into test(id, val) values (:vtp1, :vtp2)", BindVars: {#maxLimit: "type:INT64 value:\"10001\" "vtp1: "type:INT64 value:\"1\" "vtp2: "type:VARBINARY value:\"hello\" "} (errno 1062) (sqlstate 23000) during query: insert into test (id, val) values(1, 'hello')
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0xbc8724]

goroutine 109 [running]:
testing.tRunner.func1(0xc000209200)
	/usr/local/go/src/testing/testing.go:830 +0x392
panic(0xcb73c0, 0x1720750)
	/usr/local/go/src/runtime/panic.go:522 +0x1b5
vitess.io/vitess/go/vt/vtqueryserver.testDML(0xc000209200, 0xc00017b500, 0xe08139, 0x2d, 0x1, 0x1)
	/home/morgo/vitess/go/vt/vtqueryserver/endtoend_test.go:160 +0x194
vitess.io/vitess/go/vt/vtqueryserver.TestTransactions(0xc000209200)
	/home/morgo/vitess/go/vt/vtqueryserver/endtoend_test.go:258 +0x1ad
testing.tRunner(0xc000209200, 0xe2aa50)
	/usr/local/go/src/testing/testing.go:865 +0xc0
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:916 +0x35a
FAIL	vitess.io/vitess/go/vt/vtqueryserver	3.086s
ok  	vitess.io/vitess/go/vt/vttablet/customrule/filecustomrule	0.009s

Because this relates to vtqueryserver, per @gedgar 's comment in #5421 we should probably remove this utility and test rather than fix it.