kunit: remove timeout dependence on sysctl_hung_task_timeout_seconds
In discussion of how to handle timeouts, it was noted that if
sysctl_hung_task_timeout_seconds is exceeded for a kunit test,
the test task will be killed and an oops generated. This should
suffice as a means of debugging such timeout issues for now.
Hence remove use of sysctl_hung_task_timeout_secs, which has the
added benefit of avoiding the need to export that symbol from
the core kernel.