database/sql: fix TestTxStmtDeadlock test

database/sql: fix TestTxStmtDeadlock test

Drop error check because errors can be
not only ErrTxDone for tx stmt executions,
and the purpose of the test is just reproducing
deadlock.

Fixes #42259

Change-Id: I9e7105ada1403ec7064dcc1c3385b36893a1c195
Reviewed-on: https://go-review.googlesource.com/c/go/+/266097
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Emmanuel Odeke <emmanuel@orijtech.com>
TryBot-Result: Go Bot <gobot@golang.org>