Remove incorrect critical section use in dnlc_lookup

Remove incorrect critical section use in dnlc_lookup

Critical sections may not be used with (non-spin) locks.  As such,
this code was wrong, and led to a panic.
We don't see why there what synchronization they may have been
providing, so just remove them and do not replace them.

Change-Id: I5d81595a7059a91b9aad46ab0a634fa684f67325
Reviewed-on: http://gerrit.openafs.org/2373
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>