The testcase had a race in two places where a KILL QUERY is made towards a
running query in another connection. The query can complete early so the kill
is lost, and the test fails due to expecting ER_QUERY_INTERRUPTED.

Fix by removing the KILL QUERY. It is not needed, as the query completes by
itself after SHOW EXPLAIN FOR.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>