Delete rw_semaphore.wait_lock configure check

Last use of wait_lock was removed in "Linux 5.3 compat: retire
rw_tryupgrade()" (e7a99dab2b065ac2f8736a65d1b226d21754d771).

Fixes the issue reported in
https://github.com/openzfs/zfs/issues/11097#issuecomment-714532367

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Orivej Desh <orivej@gmx.fr>
Closes #11309