Remove the lock-file configuration and -X argument to named

The lock-file configuration (both from configuration file and -X
argument to named) has better alternatives nowadays.  Modern process
supervisor should be used to ensure that a single named process is
running on a given configuration.

Alternatively, it's possible to wrap the named with flock(1).

bin/tests/system/limits/clean.sh

@@ -18,5 +18,4 @@ rm -f dig.out.*
 rm -f */named.memstats
 rm -f */named.conf
 rm -f */named.run
-rm -f ns*/named.lock
 rm -f ns*/managed-keys.bind*