Fix: Change lock file location in default config file

Actually revert 0bd5fff to use the
default lock file location (`/var/lib/openvas/feed-update.lock`) again.

Using a different lock file location would also require to build
openvas-scanner with the `-DOPENVAS_FEED_LOCK_PATH` pointing to the same
path.

Reverting this change avoids that distributions are using the config
file with diverging lock files and therefore breaking the feed
synchronization.

(cherry picked from commit 891434a)

Author: bjoernricks

config/ospd-openvas.conf

@@ -4,4 +4,3 @@ socket_mode = 0o770
 unix_socket = /run/ospd/ospd-openvas.sock
 pid_file = /run/ospd/ospd-openvas.pid
 log_file = /var/log/gvm/ospd-openvas.log
-lock_file_dir = /run/ospd